[BUGFIX] Use the correct return type for method copyRecord_raw

DataHandler->copyRecord_raw can also return null.
This should be reflected in the doc header as well.

Resolves: #102098
Releases: main, 12.4, 11.5
Change-Id: Ic7a12233efd32b67f0bf25d6478a03f807a5623e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81353


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>