Add gitutils tests (#71580)

Summary:
Test PeekableIterator behavior

Add `.github/scripts/test_*.py` to list of tests run by test_tools
workflow and pin Python version to 3.7 in test_tools workflow

Change PeekableIterator inheritance from collections.abc.Iterator, to
typing.Iterator, which is a correct alias starting from Python-3.7

Pull Request resolved: https://github.com/pytorch/pytorch/pull/71580

Reviewed By: bigfootjon

Differential Revision: D33690659

Pulled By: malfet

fbshipit-source-id: 71f270b15138230772e2eed0da66cdfcb34825cc
(cherry picked from commit 42abb07396fa90272afb0b56508bd3a1f5c4ccbe)

.github/scripts/gitutils.py

@@ -1,9 +1,8 @@
 #!/usr/bin/env python3
 
 from collections import defaultdict
-from collections.abc import Iterator
 from datetime import datetime
-from typing import cast, Any, Dict, List, Optional, Tuple, Union
+from typing import cast, Any, Dict, Iterator, List, Optional, Tuple, Union
 import os
 import re