TST: Fix timestamp comparison test
- [x] closes #31175
- [x] tests added / passed
    - tests/scalar/timestamp/test_timestamp.py
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
    - Not needed for fixing a test

Thanks! @jreback think worth backporting? sure, thanks @Dr-Irv 