[BUGFIX] Always select database number in Redis Cache Backend

When using persistent connections, we need to always select the database.

Resolves: #81629
Releases: master, 8.7
Change-Id: Ia514a8ed8f04d1108263c39a21c654de4191db8b
Reviewed-on: https://review.typo3.org/53273


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Thomas Hohn <thomas@hohn.dk>
Tested-by: Thomas Hohn <thomas@hohn.dk>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>