tests: fix deprecation notice

Author: bpolaszek

src/Services/UnixTimestampNormalizer.php

@@ -23,4 +23,11 @@ public function supportsNormalization($data, string $format = null, array $conte
     {
         return $data instanceof \DateTimeInterface && true === ($context['meilisearch'] ?? null);
     }
+
+    public function getSupportedTypes(?string $format): array
+    {
+        return [
+            \DateTimeInterface::class => true, // @codeCoverageIgnore
+        ];
+    }
 }