[BUGFIX] Proper ext:form flex form finisher overrides

Fix a happy little regex to deal with "TCEforms"
removal of #97126. This should fix finisher override
FormEngine rendering.

Resolves: #101050
Related: #97126
Releases: main, 12.4
Change-Id: Ia8d893c3f3b31f7af83b3d9f2ae533b3e557f5a6
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80363


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan B�rk <stefan@buerk.tech>
Reviewed-by: Stefan B�rk <stefan@buerk.tech>