fix: CI returns 200 OK to PageNotFound

Author: kenjis

system/CodeIgniter.php

@@ -979,8 +979,7 @@ protected function display404errors(PageNotFoundException $e)
         // Display 404 Errors
         $this->response->setStatusCode($e->getCode());
 
-        echo $this->outputBufferingEnd();
-        flush();
+        $this->outputBufferingEnd();
 
         // Throws new PageNotFoundException and remove exception message on production.
         throw PageNotFoundException::forPageNotFound(