[skip changelog] Temporarily full pin Python in integration test CI workflow

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• The PR follows
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• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)

• What kind of change does this PR introduce?

Infrastructure fix

• What is the current behavior?

A bug introduced in the 3.9.7 release of Python causes a spurious failure of the test\test_lib.py::test_install_git_invalid_library integration test:

Click to expand

[gw1] FAILED test/test_lib.py::test_install_git_invalid_library 

=================================== FAILURES ===================================
_______________________ test_install_git_invalid_library _______________________
[gw1] darwin -- Python 3.9.7 /Users/runner/Library/Caches/pypoetry/virtualenvs/arduino-cli-5LFazWvB-py3.9/bin/python

run_command = <function run_command.<locals>._run at 0x105869e50>
data_dir = '/private/var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/pytest-of-runner/pytest-0/popen-gw1/ArduinoTest0'
task: Failed to run task "go:test-integration": exit status 2
downloads_dir = '/private/var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/pytest-of-runner/pytest-0/popen-gw1/ArduinoTest'

    def test_install_git_invalid_library(run_command, data_dir, downloads_dir):
        # Initialize configs to enable --zip-path flag
        env = {
            "ARDUINO_DATA_DIR": data_dir,
            "ARDUINO_DOWNLOADS_DIR": downloads_dir,
            "ARDUINO_SKETCHBOOK_DIR": data_dir,
            "ARDUINO_ENABLE_UNSAFE_LIBRARY_INSTALL": "true",
        }
        assert run_command("config init --dest-dir .", custom_env=env)
    
        # Create fake library repository
        repo_dir = Path(data_dir, "lib-without-header")
        with Repo.init(repo_dir) as repo:
            lib_properties = Path(repo_dir, "library.properties")
            lib_properties.touch()
            repo.index.add([str(lib_properties)])
>           repo.index.commit("First commit")

test/test_lib.py:957: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <git.index.base.IndexFile object at 0x105475c70>
message = 'First commit', parent_commits = None, head = True, author = None
committer = None, author_date = None, commit_date = None, skip_hooks = False

    def commit(self,
               message: str,
               parent_commits: Union[Commit_ish, None] = None,
               head: bool = True,
               author: Union[None, 'Actor'] = None,
               committer: Union[None, 'Actor'] = None,
               author_date: Union[str, None] = None,
               commit_date: Union[str, None] = None,
               skip_hooks: bool = False) -> Commit:
        """Commit the current default index file, creating a commit object.
        For more information on the arguments, see tree.commit.
    
        :note: If you have manually altered the .entries member of this instance,
               don't forget to write() your changes to disk beforehand.
               Passing skip_hooks=True is the equivalent of using `-n`
               or `--no-verify` on the command line.
        :return: Commit object representing the new commit"""
        if not skip_hooks:
            run_commit_hook('pre-commit', self)
    
            self._write_commit_editmsg(message)
            run_commit_hook('commit-msg', self, self._commit_editmsg_filepath())
            message = self._read_commit_editmsg()
            self._remove_commit_editmsg()
>       tree = self.write_tree()

../../../Library/Caches/pypoetry/virtualenvs/arduino-cli-5LFazWvB-py3.9/lib/python3.9/site-packages/git/index/base.py:1000: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <git.index.base.IndexFile object at 0x105475c70>

    def write_tree(self) -> Tree:
        """Writes this index to a corresponding Tree object into the repository's
        object database and return it.
    
        :return: Tree object representing this index
        :note: The tree will be written even if one or more objects the tree refers to
            does not yet exist in the object database. This could happen if you added
            Entries to the index directly.
        :raise ValueError: if there are no entries in the cache
        :raise UnmergedEntriesError: """
        # we obtain no lock as we just flush our contents to disk as tree
        # If we are a new index, the entries access will load our data accordingly
        mdb = MemoryDB()
        entries = self._entries_sorted()
        binsha, tree_items = write_tree_from_cache(entries, mdb, slice(0, len(entries)))
    
        # copy changed trees only
        mdb.stream_copy(mdb.sha_iter(), self.repo.odb)
    
        # note: additional deserialization could be saved if write_tree_from_cache
        # would return sorted tree entries
>       root_tree = Tree(self.repo, binsha, path='')

../../../Library/Caches/pypoetry/virtualenvs/arduino-cli-5LFazWvB-py3.9/lib/python3.9/site-packages/git/index/base.py:574: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <[AttributeError('binsha') raised in repr()] Tree object at 0x105290950>
repo = <git.repo.base.Repo '/private/var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/pytest-of-runner/pytest-0/popen-gw1/ArduinoTest0/lib-without-header/.git'>
binsha = b'm\xf9\x0b\xe8N1C;\xda\x9a\xc8\x11b\xf8D\x15\xc0\xdd\x02\xbf'
mode = 16384, path = ''

    def __init__(self, repo: 'Repo', binsha: bytes, mode: int = tree_id << 12, path: Union[PathLike, None] = None):
>       super(Tree, self).__init__(repo, binsha, mode, path)

../../../Library/Caches/pypoetry/virtualenvs/arduino-cli-5LFazWvB-py3.9/lib/python3.9/site-packages/git/objects/tree.py:215: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <[AttributeError('binsha') raised in repr()] Tree object at 0x105290950>
repo = <git.repo.base.Repo '/private/var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/pytest-of-runner/pytest-0/popen-gw1/ArduinoTest0/lib-without-header/.git'>
binsha = b'm\xf9\x0b\xe8N1C;\xda\x9a\xc8\x11b\xf8D\x15\xc0\xdd\x02\xbf'
mode = 16384, path = ''

    def __init__(self,
                 repo: 'Repo', binsha: bytes, mode: Union[None, int] = None, path: Union[None, PathLike] = None
                 ) -> None:
        """Initialize a newly instanced IndexObject
    
        :param repo: is the Repo we are located in
        :param binsha: 20 byte sha1
        :param mode:
            is the stat compatible file mode as int, use the stat module
            to evaluate the information
        :param path:
            is the path to the file in the file system, relative to the git repository root, i.e.
            file.ext or folder/other.ext
        :note:
            Path may not be set of the index object has been created directly as it cannot
            be retrieved without knowing the parent tree."""
>       super(IndexObject, self).__init__(repo, binsha)

../../../Library/Caches/pypoetry/virtualenvs/arduino-cli-5LFazWvB-py3.9/lib/python3.9/site-packages/git/objects/base.py:168: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <[AttributeError('binsha') raised in repr()] Tree object at 0x105290950>
repo = <git.repo.base.Repo '/private/var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/pytest-of-runner/pytest-0/popen-gw1/ArduinoTest0/lib-without-header/.git'>
binsha = b'm\xf9\x0b\xe8N1C;\xda\x9a\xc8\x11b\xf8D\x15\xc0\xdd\x02\xbf'

    def __init__(self, repo: 'Repo', binsha: bytes):
        """Initialize an object by identifying it by its binary sha.
        All keyword arguments will be set on demand if None.
    
        :param repo: repository this object is located in
    
        :param binsha: 20 byte SHA1"""
>       super(Object, self).__init__()

../../../Library/Caches/pypoetry/virtualenvs/arduino-cli-5LFazWvB-py3.9/lib/python3.9/site-packages/git/objects/base.py:56: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <[AttributeError('binsha') raised in repr()] Tree object at 0x105290950>
args = (), kwargs = {}

    def _no_init(self, *args, **kwargs):
>       raise TypeError('Protocols cannot be instantiated')
E       TypeError: Protocols cannot be instantiated

../../../hostedtoolcache/Python/3.9.7/x64/lib/python3.9/typing.py:1083: TypeError
=========================== short test summary info ============================
FAILED test/test_lib.py::test_install_git_invalid_library - TypeError: Protoc...
!!!!!!!!!!!!!!!!!!!!!!!!!! stopping after 1 failures !!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!! xdist.dsession.Interrupted: stopping after 1 failures !!!!!!!!!!!!!
============= 1 failed, 174 passed, 1 skipped in 784.80s (0:13:04) =============

Upstream bug report:
https://bugs.python.org/issue45121

• What is the new behavior?

As a workaround, the Python version used by the "Test Integration" CI workflow that runs the integration tests is pinned to the last working version: 3.9.6.

• Does this PR introduce a breaking change, and is
  titled accordingly?

No breaking change.

• Other information:

Since it is convenient to get automatic updates for Python patch releases, this full pin should be reverted back to the "3.9" minor version pin once a new version of Python is released with the bug fixed and added to versions available for installation via the actions/setup-python GitHub Actions action.