Fix GreetingNormalizer::normalize

`Compile Error: Declaration of App\Rest\Serializer\GreetingNormalizer::normalize(mixed $object, ?string $format = null, array $context = []): mixed must be compatible with Symfony\Component\Serializer\Normalizer\NormalizerInterface::normalize(mixed $data, ?string $format = null, array $context = []): ArrayObject|array|string|int|float|bool|null`

Author: adriendupuis

code_samples/api/rest_api/src/Rest/Serializer/GreetingNormalizer.php

@@ -17,7 +17,7 @@ public function supportsNormalization(mixed $data, ?string $format = null)
     }
 
     /** @param \App\Rest\Values\Greeting $object */
-    public function normalize(mixed $object, ?string $format = null, array $context = []): mixed
+    public function normalize(mixed $object, ?string $format = null, array $context = []): array|\ArrayObject|bool|float|int|null|string
     {
         $data = [
             'Salutation' => $object->salutation,