[1.6.x] Fixed #21122 -- Improved clean up of test temp directory on Windows

- Fixed test that didn't close the files it opened
- Caught and handled exception when temp directory cannot be removed

Backport of 978e1351a6 of master

tests/files/tests.py

@@ -175,3 +175,6 @@ class FileMoveSafeTests(unittest.TestCase):
 
         # should allow it and continue on if allow_overwrite is True
         self.assertIsNone(file_move_safe(self.file_a, self.file_b, allow_overwrite=True))
+
+        os.close(handle_a)
+        os.close(handle_b)