[BUGFIX] Fix notice in FrontendConfigurationManager

Resolves: #99213
Releases: 11.5
Change-Id: I1a664d2e4b9c84063383769f956609390e8c3021
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77371


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>