Note to contributors: This is a simple task intended for people who have NOT taken/solved a good first issue so far.

We have clean up of entries. It is spelled as "Cleanup" in JabRef, but should be "Clean up".

• Update occurrences in the code (wherever it's visible to the user)
• Update https://docs.jabref.org/finding-sorting-and-cleaning-entries/cleanupentries

Background:

• https://www.merriam-webster.com/dictionary/clean%20up
• Risen by Cleanup entries - Convert to biblatex does not work #11868