[TASK] Fix phpstan errors from ReturnTypeRule in various exts

* EXT:belog
* EXT:beuser
* EXT:dashboard
* EXT:extensionmanager

Resolves: #94256
Releases: master
Change-Id: Iee778a0a2a0ec3b92453762ea285aa7825e3b8c9
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72040


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Benni Mack <benni@typo3.org>