[BUGFIX] IRRE: Create a correct original value identifier

The value of `data-table-unique-original-value` was accidentally of type
array. This causes runtime errors since a string is expected.

This patch now creates a proper value passed to FormEngine to handle the
original unique value.

Resolves: #89588
Related: #87711
Releases: master, 9.5
Change-Id: I9184aa025f01196d0c206b5b86c712dc1049487f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62195


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Susanne Moog <look@susi.dev>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Susanne Moog <look@susi.dev>