This commit updates `phpstan/phpstan` to the latest version and fixes
one issue within `RedisSessionBackend` where the Redis API claims to
return a `\Redis` object when calling `->del()`. This indicates a usage
of multi mode, where the delete state cannot get determined.
Also, multi mode is not supported by our session backend, therefore we
handle this case as "not successful" now.

Executed command:

    composer require --dev phpstan/phpstan:^1.10.41 -W

Resolves: #102320
Releases: main, 12.4
Change-Id: I6f4edb746c6e23d92d5147cc7c711d8da0309f0f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81690


Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benni Mack <benni@typo3.org>