[BUGFIX] Allow sub directories for form definitions

Frontend and listing in the backend module allow form definitions within
subdirectories but editing a definition throws an exception because of a
too strict comparison.

Resolves: #100892
Releases: main, 12.4, 11.5
Change-Id: Ib76ce20535286b7830183111af628c686d4b0506
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79224


Tested-by: core-ci <typo3@b13.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>