[TASK] Avoid type error in FileCollector

Resolves: #104557
Releases: main, 12.4, 11.5
Change-Id: I1bea6d74fc444007c8787e0a642c86b35a7ccb90
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85538
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/frontend/Classes/Resource/FileCollector.php

@@ -221,7 +221,7 @@ static function (
                     FileInterface $b
                 ) use ($sortingProperty) {
                     if ($a->hasProperty($sortingProperty) && $b->hasProperty($sortingProperty)) {
-                        return strnatcasecmp($a->getProperty($sortingProperty), $b->getProperty($sortingProperty));
+                        return strnatcasecmp((string)$a->getProperty($sortingProperty), (string)$b->getProperty($sortingProperty));
                     }
                     return 0;
                 }