[BUGFIX] Use correct l10n_parent relation in ext:test_datahandler

There was a copy&paste leftover, leading to translated records
being related to the wrong table.

By fixing the wrong TCA configuration, sys_refindex entries in
several test fixtures had to be adjusted.

Resolves: #96025
Releases: master, 11.5
Change-Id: I197688e80e98a45a595e5304a49249ecfdcbfe91
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72230


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>