Fix method return type from closure to callable

Updated the return type of the `getLabels` method to `callable` for better type accuracy. This aligns with PHP standards and improves code clarity and maintainability.

src/Bundle/ChillPersonBundle/Export/Aggregator/AccompanyingCourseAggregators/UserWorkingOnCourseAggregator.php

@@ -54,7 +54,7 @@ final readonly class UserWorkingOnCourseAggregator implements AggregatorInterfac
         return [];
     }
 
-    public function getLabels($key, array $values, $data): closure
+    public function getLabels($key, array $values, $data): callable
     {
         return function (int|string|null $userId) {
             if (null === $userId || '' === $userId) {