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/test_gitutils.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python3
+from gitutils import PeekableIterator
+from unittest import TestCase, main
+
+class TestPeekableIterator(TestCase):
+    def test_iterator(self, input_: str = "abcdef") -> None:
+        iter_ = PeekableIterator(input_)
+        for idx, c in enumerate(iter_):
+            self.assertEqual(c, input_[idx])
+
+    def test_is_iterable(self) -> None:
+        from collections.abc import Iterator
+        iter_ = PeekableIterator("")
+        self.assertTrue(isinstance(iter_, Iterator))
+
+    def test_peek(self, input_: str = "abcdef") -> None:
+        iter_ = PeekableIterator(input_)
+        for idx, c in enumerate(iter_):
+            if idx + 1 < len(input_):
+                self.assertEqual(iter_.peek(), input_[idx + 1])
+            else:
+                self.assertTrue(iter_.peek() is None)
+
+
+
+if __name__ == '__main__':
+    main()