[BUGFIX] Prevent array to string conversion in BackendUtility

The value of an `label_alt` field might be
an array, e.g. for TCA type `select` fields.

Those values must not be formatted as this
is done by `BU::getProcessedValue()` after
resolving the correct record relation.

Resolves: #103838
Releases: main, 12.4
Change-Id: Ibfec36d2df94661fde2d82eb60bb2736205d17c3
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84334


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Johannes Schlier
Tested-by: Johannes Schlier
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Oliver Bartsch <bo@cedev.de>