CI: Unpin matplotlib

[phofl]

• closes CI: matplotlib 3.7.0 broke ci #51394 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

lets see if the new release addresses the failures

[phofl]

cc @mroeschke I think you took a closer look at the failures when 3.7 came out. Is this test failure expected and we have to fix it or is it on the matplotlib side?

[mroeschke]

I don't remember seeing UserWarning: All values for SymLogScale are below linthresh, making it effectively linear. You likely should lower the value of linthresh. in the previous release. I suppose we can catch this in our test.

For AttributeError: 'NoneType' object has no attribute 'rowspan' I think we have to address this on our side. I tried addressing it with this (undo) commit but it caused other test failures I didn't really understand :/
a36f007

[tacaswell]

#52150 fixes one of the errors.

The other failure I think you should fix by making the data range bigger with your test data or add a warning filter to that test.

[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 2.0.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 2c68dd3d9c415f40b04c500936670470c4eabd6e

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

git commit -am 'Backport PR #51990: CI: Unpin matplotlib'

4. Push to a named branch:

git push YOURFORK 2.0.x:auto-backport-of-pr-51990-on-2.0.x

5. Create a PR against branch 2.0.x, I would have named this PR:

"Backport PR #51990 on branch 2.0.x (CI: Unpin matplotlib)"

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.