fix merge

Author: xabbuh

src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php

@@ -1522,7 +1522,7 @@ protected function extractAttributes(object $object, ?string $format = null, arr
         return [];
     }
 
-    protected function getAttributeValue(object $object, string $attribute, ?string $format = null, array $context = [])
+    protected function getAttributeValue(object $object, string $attribute, ?string $format = null, array $context = []): mixed
     {
         return null;
     }