ci: fix broken configuration

[henryiii]

I'm not sure how this ever passed, but:

      run: python -m pip install pytest
           pip install --verbose .

is exactly the same as

      run: python -m pip install pytest pip install --verbose .

in YAML. If you used a YAML formatter, say in pre-commit, it would have rewritten this for you and it would have been obvious that it was incorrect. Currently it's failing because there is no install package, maybe there used to be such a package and it got removed?

This should fix #51 and #52.

[wjakob]

Thank you!