Fix Quantity & Unit is_compatible_with with registry active contexts

[jules-ch]

• Closes is_compatible_with ignores active contexts #1424
• Executed pre-commit run --all-files with no errors
• The change is fully covered by automated unit tests
• Documented in docs/ as appropriate
• Added an entry to the CHANGES file

[keewis]

wow, that was an easy fix. Thanks! It might be good to add tests, though?

[jules-ch]

I forgot to push them, I'll do that tomorrow