[BUGFIX] DB check > Search: Convert `--div--` to optgroup

Querying the database for the placeholder `--div--` is rather pointless,
thus this possibility is removed. Instead, the placeholder is converted
into an optgroup.

Resolves: #87976
Releases: master, 9.5
Change-Id: I60729a3fae1bc37c12612fccf0f8491ad27d8908
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/60305


Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Henrik Elsner <helsner@dfau.de>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Henrik Elsner <helsner@dfau.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>