enable --pretty by default

[mkaraev]

closes #19108

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

[wyattscarpenter]

You have a large number of test failures here, presumably because a bunch of expected errors have switched to giving the pretty error messages now!

These will need to be resolved before this pull request can be accepted. There's some kind of flag to make pytest update all the tests, but I've never used it; I just know about it because on test failures it prints this little message: Update the test output using --update-data (implies -n0; you can additionally use the -k selector to update only specific tests. You should probably also give all of those changes a cursory manual review, as well, but I suppose that comes down to how confident you feel. (Especially review ones that actually test the pretty flag, to make sure the new way the flag works actually works.) I suppose another solution would be to give the no-pretty specification explicitly to all of these tests, although I see little reason why that would be preferable.

[mkaraev]

@wyattscarpenter okay, I will check how tests could be updated