Exclude pydata-sphinx-theme 0.13.0 since the build isn't working with it

[tomwhite]

• Fixes Sphinx build is failing with extension error (pydata_sphinx_theme) #1037

[codecov-commenter]

Codecov Report

Merging #1038 (0ef7af2) into main (d4780b6) will not change coverage.
The diff coverage is n/a.

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@@            Coverage Diff            @@
##              main     #1038   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           44        44           
  Lines         4534      4529    -5     
=========================================
- Hits          4534      4529    -5     

Impacted Files	Coverage Δ
sgkit/display.py	100.00% <0.00%> (ø)
sgkit/variables.py	100.00% <0.00%> (ø)
sgkit/stats/aggregation.py	100.00% <0.00%> (ø)

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[tomwhite]

Closing in favour of #1041