Fix Inspector tests for Matplotlib 3.6 compatibility

[hoechenberger]

Fixes #1068

Merge checklist

Maintainer, please confirm the following before merging.
If applicable:

• All comments are resolved
• This is not your own PR
• All CIs are happy
• PR title starts with [MRG]
• whats_new.rst is updated
• New contributors have been added to CITATION.cff
• PR description includes phrase "closes <#issue-number>"

[hoechenberger]

Failing tests must be fixed upstream in MNE.

[sappelhoff]

the doc build issue is due to mne-tools/mne-python#11207

I'll try to push a fix here

[sappelhoff]

@hoechenberger feel free to take out of draft status and merge when you are ready :-)

thanks for the fix

[codecov]

Codecov Report

Merging #1069 (b67548f) into main (22cbd10) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1069   +/-   ##
=======================================
  Coverage   95.01%   95.01%           
=======================================
  Files          24       24           
  Lines        3835     3835           
=======================================
  Hits         3644     3644           
  Misses        191      191           

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[hoechenberger]

I don't have time to work on the upstream changes. We can just leave this PR open until stuff gets fixed upstream, or we merge to already reduce the number of failing tests we see here. WDYT?

[sappelhoff]

merging, this is totally fine - thanks