Use assertEqual instead of assertEquals for Python 3.12 compatibility.

[tirkarthi]

https://docs.python.org/3.12/whatsnew/3.12.html#removed . This method was removed in Python 3.12

[bskinn]

Thanks for the PR! I think I remember seeing this.

Looks like you've done a pretty thorough job, but to be sure: Have you checked the entire test suite for this deprecated usage?

Is the new method available in Python 3.6+? (There are jobs in the CI that test on 3.6, so I'm guessing this is all good, but want to specifically ask.)

This is worth a CHANGELOG entry -- please add one, if you would.

[bskinn]

It looks like @mgorny found two more instances that needed replacement in #2275. Closing this PR in favor of that one. Thank you for this PR, though, @tirkarthi!