gh-140774: Fix pathlib.Path.chmod handling of Windows Archive bit

[pareshjoshij]

Fixes #140774.

On Windows, Path.chmod(mode, follow_symlinks=True) fails silently (does not change permissions) if the target file has its Archive bit cleared. This issue arises because passing a Path object directly to os.chmod triggers a behavior difference in the Windows implementation compared to passing a raw string.

The Fix:
Updated Lib/pathlib/__init__.py to explicitly cast the path to a string (str(self)) before passing it to os.chmod.

Verification:
Added a regression test test_chmod_archive_bit_behavior to WindowsPathTest in Lib/test/test_pathlib/test_pathlib.py. The test:

1. Creates a temporary file.
2. Manually clears the Archive bit using the Windows attrib command.
3. Verifies that chmod successfully removes the Read-Only attribute.

• Issue: Path.chmod() silently fails on Windows when archive bit is cleared and follow_symlinks=True #140774