[BUGFIX] Use correct regular expression in FormDefinitionConversionService

Resolves: #92362
Releases: master, 10.4, 9.5
Change-Id: I9db655907b321bce70285e3201e8ea6a3bd205f3
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/66019


Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Björn Jacob <bjoern.jacob@tritum.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Björn Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>