Fix exception formatting by calling array_keys()

Author: nathan-d-h

src/Symfony/Doctrine/EventListener/PublishMercureUpdatesListener.php

@@ -189,7 +189,7 @@ private function storeObjectToPublish(object $object, string $property): void
 
         foreach ($options as $key => $value) {
             if (!isset(self::ALLOWED_KEYS[$key])) {
-                throw new InvalidArgumentException(\sprintf('The option "%s" set in the "mercure" attribute of the "%s" resource does not exist. Existing options: "%s"', $key, $resourceClass, implode('", "', array_keys(self::ALLOWED_KEYS))));
+                throw new InvalidArgumentException(\sprintf('The option "%s" set in the "mercure" attribute of the "%s" resource does not exist. Existing options: "%s"', $key, $resourceClass, implode('", "', \array_keys(self::ALLOWED_KEYS))));
             }
         }