[CLEANUP] Category related tests cleanup

The category registry test and makeCategorizable
test of extension management utility are cleaned up
to use proper naming and actually test what
is in their scope.

Resolves: #57949
Releases: 6.2
Change-Id: I5dae812435d71b5188b4dc8ecf9dd2ce9d400658
Reviewed-on: https://review.typo3.org/29488
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel