Update pytest.yml

[arm61]

Remove the coveralls part of the Github action.

[aglavic]

We could use coverage.py to run something similar as a github action. There is an output as html with detailed information that one might add to the docs, too.

I found this in a quick search: https://nedbatchelder.com/blog/202209/making_a_coverage_badge.html

[bmaranville]

I tested the coverage.py solution you suggested here: https://bmaranville.github.io/orsopy/coverage/
It only takes a little bit of extra code in the action that builds the docs (builds the coverage document first), and we could of course add a link to the coverage report on the front page of the documentation.

I'm worried that the badge solution in that link is a little flimsy (storing state in a gist, requiring secrets, etc) and might require a lot more maintenance than the HTML output directly by coverage.py.

[arm61]

@bmaranville and @aglavic do we want to merge this?