[BUGFIX] Cast URI to string to allow json encoding

Otherwise the PHP object is transformed to an empty JS object
instead of a string containing the actual URI

Resolves: #105036
Releases: main, 12.4, 11.5
Change-Id: I083524291d5e86869e3989a4836d2321a133c36f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/86186


Tested-by: Garvin Hicking <gh@faktor-e.de>
Tested-by: Andreas Kienast <akienast@scripting-base.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Andreas Kienast <akienast@scripting-base.de>
(cherry picked from commit e7b35525)
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/86212