Backport PR #3462 on branch 1.11.x ((chore): Simplify BasePlot’s var_groups)

[meeseeksmachine]

Backport PR #3462: (chore): Simplify BasePlot’s var_groups

[codecov]

Codecov Report

Attention: Patch coverage is 80.85106% with 9 lines in your changes missing coverage. Please review.

Project coverage is 75.50%. Comparing base (a28fe88) to head (241e755).
Report is 2 commits behind head on 1.11.x.

Files with missing lines	Patch %	Lines
src/scanpy/plotting/_baseplot_class.py	80.43%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           1.11.x    #3471      +/-   ##
==========================================
+ Coverage   75.44%   75.50%   +0.05%     
==========================================
  Files         113      113              
  Lines       13250    13318      +68     
==========================================
+ Hits         9997    10056      +59     
- Misses       3253     3262       +9     

Files with missing lines	Coverage Δ
src/scanpy/neighbors/_connectivity.py	85.96% <100.00%> (ø)
src/scanpy/plotting/_baseplot_class.py	89.56% <80.43%> (-1.99%)	⬇️

... and 1 file with indirect coverage changes