Merge branch '6.1' into 6.2

* 6.1:
  [Notifier] Add PushNotificationInterface to the list of interfaces to customize a notification

Author: javiereguiluz

notifier.rst

@@ -697,9 +697,10 @@ and its ``asChatMessage()`` method::
     }
 
 The
-:class:`Symfony\\Component\\Notifier\\Notification\\SmsNotificationInterface`
-and
+:class:`Symfony\\Component\\Notifier\\Notification\\SmsNotificationInterface`,
 :class:`Symfony\\Component\\Notifier\\Notification\\EmailNotificationInterface`
+and
+:class:`Symfony\\Component\\Notifier\\Notification\\PushNotificationInterface`
 also exists to modify messages sent to those channels.
 
 Customize Browser Notifications (Flash Messages)