Issue #3281424: Type error in ScheduledMaintenanceSubscriber::checkForScheduledMaintenance().

  /**

   * Checks if a scheduled maintenance should be started.

   *

   * @param \Symfony\Component\HttpKernel\Event\RequestEvent $event

   * @param \Symfony\Component\HttpKernel\Event\GetResponseEvent|\Symfony\Component\HttpKernel\Event\RequestEvent $event

   *   The request event.

   */

  public function checkForScheduledMaintenance(RequestEvent $event) {

  public function checkForScheduledMaintenance($event) {

    // Get maintenance mode state.

    $maintenance_mode = $this->state->get('system.maintenance_mode');