[skip changelog] Fix integration tests by setting a maximum python version

[silvanocerza]

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• The PR has no duplicates (please search among the Pull Requests
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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?

Fixes an issue with Python integration tests.

• What is the current behavior?

Integration tests are failing because a library has issue with Python 3.9.7.

Failing workflow: https://github.com/arduino/arduino-cli/runs/3698900893?check_suite_focus=true

• What is the new behavior?

Constrain maximum Python version usable to be equal or greater than 3.8 and older than 3.9.7 to stop integration tests from failing.

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

Nope.

• Other information:

Probably related to gitpython-developers/GitPython#1341.

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See how to contribute

[per1234]

@silvanocerza I fixed this previously with #1442 but it wasn't cherry-picked into the 0.19.1-rc2 branch:
https://github.com/arduino/arduino-cli/blob/0.19.1-rc2/.github/workflows/test-go-integration-task.yml#L8

But I think this is still an important change to do to fix the issue for running the tests locally. I didn't consider that side of things.

[silvanocerza]

Ah! I completely missed that PR, I was kinda confused why it was failing today but not yesterday. Now it makes sense, thanks Per.