[BUGFIX] Fix insufficient mocking in ContentObjectRenderer

Resolves: #59967
Releases: 6.3, 6.2
Change-Id: Ie30b8e522f9045c7cd6cbe9c032413c0ad936b1a
Reviewed-on: https://review.typo3.org/31205
Reviewed-by: Markus Klein
Tested-by: Markus Klein