[TASK] Convert DataMapperTest to functional

Resolves: #98897
Releases: main
Change-Id: I5f4d861dc67a6858050564b5ec31a88383d01e2a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76918


Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>