Fix GreetingInputDenormalizer::denormalize

`Compile Error: Declaration of App\Rest\Serializer\GreetingInputDenormalizer::denormalize(mixed $data, string $type, ?string $format = null, array $context = []) must be compatible with Symfony\Component\Serializer\Normalizer\DenormalizerInterface::denormalize(mixed $data, string $type, ?string $format = null, array $context = []): mixed`

Author: adriendupuis

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

@@ -11,7 +11,7 @@ class GreetingInputDenormalizer implements DenormalizerInterface, DenormalizerAw
 {
     use DenormalizerAwareTrait;
 
-    public function denormalize(mixed $data, string $type, ?string $format = null, array $context = [])
+    public function denormalize(mixed $data, string $type, ?string $format = null, array $context = []): mixed
     {
         if ('json' === $format) {
             $data = $data[array_key_first($data)];