[BUGFIX] Fix tests for old property mapper

The "fix" for failing tests after merging #42622
was to actually not test if the mapping works,
but only if the map method completes without errors.

Re-enable the correct test again.

Fixes: #45682
Releases: 6.1
Change-Id: I8ddabb1fce82f75b379c41aac7c959890f3ff56b
Reviewed-on: https://review.typo3.org/18462
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring