Preventing the Python 3.12's "Deprecated since version 3.12: Use datetime.now() with UTC instead."

[Lisias]

Description

See https://github.com/webrecorder/pywb/issues/913

Types of changes

• [ ] Replay fix (fixes a replay specific issue)
• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added or updated tests to cover my changes.
• [ ] All new and existing tests passed.