Default to true for _api_respond attribute

Co-Authored-By: teohhanhui <[email protected]>

Author: antograssiot

src/EventListener/SerializeListener.php

@@ -47,7 +47,7 @@ public function onKernelView(GetResponseForControllerResultEvent $event)
         $controllerResult = $event->getControllerResult();
         $request = $event->getRequest();
 
-        if ($controllerResult instanceof Response || !$request->attributes->get('_api_respond')) {
+        if ($controllerResult instanceof Response || !$request->attributes->get('_api_respond', true)) {
             return;
         }