[BUGFIX] Fix undefined array key warnings in DatabaseIntegrityController

Since #99739 the TCA types select, radio and check use associative
array keys for their items.

In ext:lowlevel DatabaseIntegrityController, some functions still access
indexed array keys, which leads to a PHP warning.

This change ensures that the associative array keys introduced in #99739
are used.

Resolves: #100521
Releases: main
Signed-off-by: Torben Hansen <derhansen@gmail.com>
Change-Id: I285215730bc391d7db6c795dbbdd9b1b0b9d447b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78529


Tested-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan Bürk <stefan@buerk.tech>