[BUGFIX] Fix undefined array key warning in TcaInline

Resolves: #97461
Releases: main, 11.5
Change-Id: I4c16d9546bd878bb84d2457e2a706829d8232e7c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74397


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>