Add return type for getTargets() method in validator

Ensure the `getTargets()` method specifies its return type for better code clarity and type safety. This update aligns with modern PHP practices and improves maintainability.

src/Bundle/ChillPersonBundle/Validator/Constraints/AccompanyingPeriod/ConfidentialCourseMustHaveReferrer.php

@@ -18,6 +18,9 @@ class ConfidentialCourseMustHaveReferrer extends Constraint
 {
     public string $message = 'A confidential parcours must have a referrer';
 
+    /**
+     * @return array<string>
+     */
     public function getTargets(): array
     {
         return [self::CLASS_CONSTRAINT];