Update HeatMap and QuadMesh test to pass on Matplotlib 3.8

[Hoxbro]

Fixes #5896

It needs #5910 to be fully compatible with Matplotlib 3.8.

[codecov-commenter]

Codecov Report

Merging #5924 (e72c496) into main (3da3d75) will decrease coverage by 0.01%.
The diff coverage is 82.35%.

@@            Coverage Diff             @@
##             main    #5924      +/-   ##
==========================================
- Coverage   88.58%   88.57%   -0.01%     
==========================================
  Files         315      315              
  Lines       65442    65460      +18     
==========================================
+ Hits        57972    57984      +12     
- Misses       7470     7476       +6     

Flag	Coverage Δ
ui-tests	23.16% <14.70%> (-0.01%)	⬇️

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Files	Coverage Δ
holoviews/tests/plotting/matplotlib/test_plot.py	100.00% <100.00%> (ø)
...iews/tests/plotting/matplotlib/test_heatmapplot.py	91.42% <76.92%> (-8.58%)	⬇️
...ews/tests/plotting/matplotlib/test_quadmeshplot.py	92.85% <83.33%> (-7.15%)	⬇️

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[Hoxbro]

percent_bachelors_degrees_women_usa.csv is removed in Matplotlib 3.8 ref, so I have uploaded it to datasets.holoviz.org now.