Fix phpstan DI issues

Problem/Motivation

The PHPStan scan identifies the following issues:

 ------ ---------------------------------------------------------------------- 
  Line   src/EventSubscriber/ResponseSubscriber.php                            
 ------ ---------------------------------------------------------------------- 
  47     \Drupal calls should be avoided in classes, use dependency injection  
         instead                                                               
  53     \Drupal calls should be avoided in classes, use dependency injection  
         instead                                                               
 ------ ---------------------------------------------------------------------- 

Let's fix these.