Fix IndexFile.commit parent_commits annotation

This changes that parameter's annotation to be equivalent to the
annotation of the corresponding Commit.create_from_tree parameter.

It had been annotated as the old Commit_ish type, but it passes
that argument to Commit.create_from_tree, and it also refers to
that method in its docstring for usage. Commit.create_from_tree
annotates this argument as an optional list of Commit objects, and
if the objects obtained when it iterates them are not Commit
instances, then an exception is raised. Even if being able to pass
other commit-ish things (or references, strings, etc.) is
desirable, that does not currently work.

This also improves sorting (and grouping style) of imports in that
file (which were being changed already to no longer import the old
Commit_ish type).

Author: EliahKagan

Diff for: git/index/base.py

@@ -11,23 +11,16 @@
 import glob
 from io import BytesIO
 import os
+import os.path as osp
 from stat import S_ISLNK
 import subprocess
 import sys
 import tempfile
 
-from git.compat import (
-    force_bytes,
-    defenc,
-)
-from git.exc import GitCommandError, CheckoutError, GitError, InvalidGitRepositoryError
-from git.objects import (
-    Blob,
-    Submodule,
-    Tree,
-    Object,
-    Commit,
-)
+from git.compat import defenc, force_bytes
+import git.diff as git_diff
+from git.exc import CheckoutError, GitCommandError, GitError, InvalidGitRepositoryError
+from git.objects import Blob, Commit, Object, Submodule, Tree
 from git.objects.util import Serializable
 from git.util import (
     LazyMixin,
@@ -41,24 +34,17 @@
 from gitdb.base import IStream
 from gitdb.db import MemoryDB
 
-import git.diff as git_diff
-import os.path as osp
-
 from .fun import (
+    S_IFGITLINK,
+    aggressive_tree_merge,
     entry_key,
-    write_cache,
     read_cache,
-    aggressive_tree_merge,
-    write_tree_from_cache,
-    stat_mode_to_index_mode,
-    S_IFGITLINK,
     run_commit_hook,
+    stat_mode_to_index_mode,
+    write_cache,
+    write_tree_from_cache,
 )
-from .typ import (
-    BaseIndexEntry,
-    IndexEntry,
-    StageType,
-)
+from .typ import BaseIndexEntry, IndexEntry, StageType
 from .util import TemporaryFileSwap, post_clear_cache, default_index, git_working_dir
 
 # typing -----------------------------------------------------------------------------
@@ -80,12 +66,13 @@
     Union,
 )
 
-from git.types import Old_commit_ish, Literal, PathLike
+from git.types import Literal, PathLike
 
 if TYPE_CHECKING:
     from subprocess import Popen
-    from git.repo import Repo
+
     from git.refs.reference import Reference
+    from git.repo import Repo
     from git.util import Actor
 
 
@@ -1127,7 +1114,7 @@ def move(
     def commit(
         self,
         message: str,
-        parent_commits: Union[Old_commit_ish, None] = None,
+        parent_commits: Union[List[Commit], None] = None,
         head: bool = True,
         author: Union[None, "Actor"] = None,
         committer: Union[None, "Actor"] = None,