[BUGFIX] Add missing StringUtility in ContentObjectRenderer

The import was removed shortly before
https://review.typo3.org/c/Packages/TYPO3.CMS/+/71032 was merged so
it's added again.

Resolves: #95321
Related: #95189
Related: #95190
Releases: master
Change-Id: If44ba57ab6a390fac07c1ee12bbd8f36d2e7539f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71191


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>