MAINT: Sphinx 4 and Python 3.10 in GitHub tests

[choldgraf]

This bumps our GHA test suite to use Sphinx 4 as a follow up to #1448 - it also adds a Python 3.10 test to the matrix. Let's see if tests pass.

[mmcky]

@choldgraf if this is branched from the latest master there are some broken myst-nb links that throw warnings that are fixed in #1494

So we could merge #1494 and then merge this given it's maintenance on the github repo testing infrastructure.

[choldgraf]

@mmcky gotcha - the main thing is that we need to make sure that the tests are actually passing with Sphinx 4, since we didn't add that to our github action in #1448 - if they do pass, and the only fails are the missing links that you've fixed in #1494 - then I'd be +1 on merging this and you can re-base on #1494 to make sure the tests are still passing there. Does that make sense?

[mmcky]

@mmcky gotcha - the main thing is that we need to make sure that the tests are actually passing with Sphinx 4, since we didn't add that to our github action in #1448 - if they do pass, and the only fails are the missing links that you've fixed in #1494 - then I'd be +1 on merging this and you can re-base on #1494 to make sure the tests are still passing there. Does that make sense?

Yeah I noticed that you updated that. I have been testing in tox locally but completely agree on that change

[choldgraf]

It looks like Python 3.10 isn't easily supported out of the box (unless somebody can decipher https://github.com/executablebooks/jupyter-book/pull/1509/checks?check_run_id=3901065796), maybe we'll need to wait for another package to be upgraded (I liked @chrisjsewell's idea that we only commit to supporting new versions within ~ 6 months of its release).

In that case, I think @mmcky you should add https://github.com/executablebooks/jupyter-book/pull/1509/files#diff-1db27d93186e46d3b441ece35801b244db8ee144ff1405ca27a163bfe878957fL86-R87 to your PR in #1494 and we can track the Python 3.10 support in a future release.

[mmcky]

I agree I will move the needed changes @choldgraf

[codecov]

Codecov Report

Merging #1509 (4f93cf0) into master (3173b00) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1509   +/-   ##
=======================================
  Coverage   91.17%   91.17%           
=======================================
  Files           7        7           
  Lines         680      680           
=======================================
  Hits          620      620           
  Misses         60       60           

Flag	Coverage Δ
pytests	91.17% <ø> (ø)

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[choldgraf]

the failing test in 3.10 might be related to pytest-dev/pytest#8546

just realized that we are using an old version of pytest...I'm not sure why we've pinned that one, but let's try bumping to the latest version and see if that fixes this

edit: upgrading pytest is also not trivial, I'll update the PR about Python 3.10 and close this