Raise phpstan to include latest phpstan bugfixes.
See: https://github.com/phpstan/phpstan/releases/tag/1.6.9

Used commands:

> composer req phpstan/phpstan:^1.6.9 --dev
> Build/Scripts/runTests.sh -s clean ; \
  Build/Scripts/runTests.sh -s phpstanGenerateBaseline

Resolves: #97668
Releases: main, 11.5
Change-Id: I61298c1696b14a6e89ddc98043de13acb127c6a0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74720


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>