[BUGFIX] Force type in ckeditor configuration migration

To avoid exceptions during the ckeditor migration the type is forced
to be a string.

Resolves: #102521
Releases: main, 12.4
Change-Id: Icfdedb5b6ef74720e8f7da205a66115bc6d7a39a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81909
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>

typo3/sysext/core/Classes/Configuration/CKEditor5Migrator.php

@@ -763,6 +763,7 @@ protected function migrateAllowedContent(): void
             foreach ($config4 as $name => $options) {
                 $config = [];
                 if ($name !== '*') {
+                    $name = (string)$name;
                     $config['name'] = str_contains($name, '*') || str_contains($name, ' ') ?
                         [ 'pattern' => str_replace(['*', ' '], ['.+', '|'], $name) ] :
                         $name;