Port over the get_cmap fix from mdakit-hole2

[IAlibay]

See: https://github.com/MDAnalysis/hole2-mdakit/pull/39/files

We might need to consider if removing hole2 and just optionally importing hole2-mdakit might be a good idea eventually.

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📚 Documentation preview 📚: https://mdanalysis--4338.org.readthedocs.build/en/4338/

[github-actions]

Linter Bot Results:

Hi @IAlibay! Thanks for making this PR. We linted your code and found the following:

There are currently no issues detected! 🎉

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cb26ebc) 93.37% compared to head (8c2c072) 93.37%.
Report is 3 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff             @@
##           develop    #4338     +/-   ##
==========================================
  Coverage    93.37%   93.37%             
==========================================
  Files          170      184     +14     
  Lines        22299    23407   +1108     
  Branches      4075     4075             
==========================================
+ Hits         20822    21857   +1035     
- Misses         962     1035     +73     
  Partials       515      515             

Files	Coverage Δ
package/MDAnalysis/analysis/hole2/hole.py	83.07% <100.00%> (ø)

... and 14 files with indirect coverage changes

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[RMeli]

LGTM, thanks @IAlibay