[BUGFIX] ParentCategory is not persisted during import

Call categoryRepository->update() after setting parentCategory

Fixes: #50281
Change-Id: Iecccbfb7309df4f0ff3b6bee24debddc48843fe0
Reviewed-on: https://review.typo3.org/22484
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer