MNT: Run PTH flake test in prep for supporting pathlib (cosmology) - #16925

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👋 Thank you for your draft pull request! Do you know that you can use [ci skip] or [skip ci] in your commit messages to skip running continuous integration tests until you are ready?

@nstarman , if this does not need a change log after all, feel free to put the no-changelog-entry-needed label back and approve and merge. Thanks!

The pre-commit failures are real.

fixed