[BUGFIX] Avoid undefined array key "enableMetaphoneSearch"

Resolves: #100883
Releases: main, 12.4, 11.5
Change-Id: I89f566a1bdf45f214a175cd389ef143c6334cda3
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79056


Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>