fix(jsonapi): restore getSupportedTypes override in ItemNormalizer

The normalizer/denormalizer split accidentally dropped this override.
Without it, JsonApi\Serializer\ItemNormalizer inherits the parent's
generic implementation (returns ['object' => false] for any format),
which breaks Symfony Serializer fast-path routing — a more generic
normalizer can win for formats that should land on the JSON:API one.

Restored to the same shape kept by JsonLd\Serializer\ItemNormalizer
post-split, matching the pre-split behavior.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: soyuka

src/JsonApi/Serializer/ItemNormalizer.php

@@ -86,6 +86,11 @@ public function supportsNormalization(mixed $data, ?string $format = null, array
         return self::FORMAT === $format && parent::supportsNormalization($data, $format, $context) && !($data instanceof \Exception || $data instanceof FlattenException);
     }
 
+    public function getSupportedTypes(?string $format): array
+    {
+        return self::FORMAT === $format ? parent::getSupportedTypes($format) : [];
+    }
+
     public function denormalize(mixed $data, string $type, ?string $format = null, array $context = []): mixed
     {
         trigger_deprecation('api-platform/core', '4.4', 'Calling "denormalize()" on "%s" is deprecated, use "%s" instead.', self::class, ItemDenormalizer::class);