Improve test suite: ridgeplot._hist

[tpvasconcelos]

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[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (2eaff20) to head (064d808).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #365   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           18        18           
  Lines          657       657           
  Branches        85        85           
=========================================
  Hits           657       657           

Flag	Coverage Δ
combined-src	100.00% <ø> (ø)

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