ensure all plots share the same hue

[dschwoerer]

by specifing vmin and vmax, the colorbar is the correct one for all
subplots

• Closes scatter plot with row or col gets hue wrong #4975
• Tests added
• Passes pre-commit run --all-files
• User visible changes (including notable bug fixes) are documented in whats-new.rst
• New functions/methods are listed in api.rst

[max-sixty]

Hi @dschwoerer — thanks for the PR, and forgive us taking a few days to review it.

Without me being an expert in this area, it looks good.

Could you add a test for the behavior?

[keewis]

this has already been fixed on master (see #4975), but tests would still be good. @dschwoerer, if you're up for writing those feel free to reuse this PR.

[max-sixty]

Closing but please feel free to reopen, thanks @dschwoerer for doing the work.