[BUGFIX] Fix PHP 8 warning in TcaFlexProcess

Resolves: #95987
Releases: master
Change-Id: Icd868d64e0414fa295f1d03c7cbe102b388ff978
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72182


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>