Fix pytest 8 compat

[flying-sheep]

• Closes pytest 8 compatibility #2836
• Tests included or not required because:

• Release notes not necessary because: dev change

Changes:

• Removes import-time change to globals:
  • matplotlib.testing:setup should be called before each (plotting) test
  • sc.set_figure_params(dpi=40, color_map="viridis") seems to be overwritten. When calling it inline, it messes up the figure params
  • sc.pl.set_rcParams_defaults() is redundant, setup from above does that.
• Use workaround from Pytest 8.0.0rc1 stopped respecting usefixtures marker applied in pytest_itemcollected pytest-dev/pytest#11759 (comment)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8986921) 72.85% compared to head (d184a9f) 73.67%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2838      +/-   ##
==========================================
+ Coverage   72.85%   73.67%   +0.82%     
==========================================
  Files         111      111              
  Lines       12383    12386       +3     
==========================================
+ Hits         9022     9126     +104     
+ Misses       3361     3260     -101     

Files	Coverage Δ
scanpy/testing/_doctests.py	80.00% <100.00%> (ø)
scanpy/testing/_pytest/__init__.py	100.00% <100.00%> (ø)
scanpy/testing/_pytest/fixtures/__init__.py	96.66% <100.00%> (ø)

... and 2 files with indirect coverage changes

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 1.9.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 330a099ffe76286f0f047387701af7e9fd58831a

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #2838: Fix pytest 8 compat'

4. Push to a named branch:

git push YOURFORK 1.9.x:auto-backport-of-pr-2838-on-1.9.x

5. Create a PR against branch 1.9.x, I would have named this PR:

"Backport PR #2838 on branch 1.9.x (Fix pytest 8 compat)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.