gh-63882: Use self.assert* in test_minidom

[StanFromIreland]

Replaces all single line asserts, all the old confirms that have multiple lines will be in another pr as the diff is harder to view.

Once raised in #63882 (comment):

In fact, having looked at the test module in a bit more detail, it's in pretty sore need of an overall modernization.

And also a few times in #132879

Request: @picnixz , @hugovk , @zware

• Issue: test_minidom has many empty tests #63882

[picnixz]

When there are assertTrue(not ...), use assertFalse, and when there are assertTrue(x is y), use assertIs. In addition, confirm() may have more than 1 conditions so they should be broken down.

[bedevere-app]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[StanFromIreland]

I messed up and re-ran a broken script after, causing some issues. Sent a fixup

[StanFromIreland]

That should be all now, I hope…

[picnixz]

Whenever there is "is(X, None)", use assertIsNone. I won't correct more.

[StanFromIreland]

Thanks :-)

[hugovk]

And backport?

[picnixz]

Mmh, yes backports can be done to ease future bps

[miss-islington-app]

Thanks @StanFromIreland for the PR, and @picnixz for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

[bedevere-app]

GH-133024 is a backport of this pull request to the 3.13 branch.