Fix GreetingNormalizer::getSupportedTypes

`Error: Class App\Rest\Serializer\GreetingNormalizer contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (Symfony\Component\Serializer\Normalizer\NormalizerInterface::getSupportedTypes)`

Author: adriendupuis

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

@@ -30,4 +30,11 @@ public function normalize(mixed $object, ?string $format = null, array $context
 
         return $this->normalizer->normalize($data, $format, $context);
     }
+
+    public function getSupportedTypes(?string $format): array
+    {
+        return [
+            Greeting::class => true,
+        ];
+    }
 }