[TASK] Show explain selection in DB check only for Mysql

As the selection "explain" only works for Mysql, it should also only be
displayed then.

Resolves: #99512
Releases: main, 11.5
Change-Id: I93ddf86d1f63ef124feb2b72e86f32d8260ad99f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77395


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>