[BUGFIX] Fix unknown keys in arrays

Fixes PHP 8-related array access errors in ContentContentObject
and AbstractMenuContentObject.

Resolves: #95453
Releases: master
Change-Id: Ic618200102720fe515236d2c9c292b684556f9cc
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71421


Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: crell <larry@garfieldtech.com>
Reviewed-by: Benni Mack <benni@typo3.org>