TST: GH30999 Add match=msg to test_nat_comparisons_invalid
This pull request xref #30999 to remove bare pytest.raises. It doesn't close that issue as I have only addressed one file: pandas/tests/scalar/test_nat.py . In that file there was only one test that had a bare pytest.raises and I added a message to the two instances of pytest.raises in that test. It required modifications to the test parameters in order to populate the message.

I did not add a whatsnew entry since it's only a tiny change to one test. Let me know if I should add one (and I am a bit unclear on how, i.e. what version this would end up in).

This is my first ever pull request to an open source project. I am expecting that I will have to make changes before it's accepted; thanks for your patience.

- [ ] xref #30999
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

thanks @moink 