comp(matplotlib): Add compatibility with Matplotlib 3.9

[hoxbro]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 70.49180% with 18 lines in your changes missing coverage. Please review.

Project coverage is 88.49%. Comparing base (e5f7aed) to head (e3e951d).

Files	Patch %	Lines
...s/tests/plotting/matplotlib/test_annotationplot.py	76.66%	7 Missing ⚠️
holoviews/plotting/mpl/chart.py	37.50%	5 Missing ⚠️
holoviews/plotting/mpl/stats.py	70.00%	3 Missing ⚠️
...views/tests/plotting/matplotlib/test_violinplot.py	71.42%	2 Missing ⚠️
...views/tests/plotting/matplotlib/test_boxwhisker.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6307      +/-   ##
==========================================
- Coverage   88.52%   88.49%   -0.04%     
==========================================
  Files         323      323              
  Lines       67999    68031      +32     
==========================================
+ Hits        60196    60202       +6     
- Misses       7803     7829      +26     

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