Fix tests to handle Python 3.13 stripping indents from docstrings

[musicinmybrain]

https://docs.python.org/3.13/whatsnew/3.13.html#other-language-changes

https://github.com/python/cpython/issues/81283

You can reproduce the original failure and verify this change by running

tox -e py313-unit

but you will need to apply https://github.com/wolever/parameterized/pull/169 first.