[BUGFIX] Prevent Undefined array key `debugMode` in Indexer

Resolves: #102383
Releases: main, 12.4, 11.5
Change-Id: Iced9d71874a51ee321857b662fa157ca2c2c0307
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82258


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>