[BUGFIX] Fix PHP 8.0 warnings in Workspace preview

Resolves: #95973
Releases: master
Change-Id: I6f0358cfdc38aff55ce8e0ef4343cd50104d93c3
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72171


Tested-by: core-ci <typo3@b13.com>
Tested-by: Achim Fritz <af@achimfritz.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Achim Fritz <af@achimfritz.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>