[ticket/14670] Set shared flag instead of defining prototype scope

The prototype scope was deprecated in symfony 2.8 and removed in 3.0.

PHPBB3-14670

tests/notification/fixtures/services_notification.yml

@@ -70,7 +70,7 @@ services:
 
     test:
         class: phpbb\notification\type\test
-        scope: prototype
+        shared: false
         parent: notification.type.base
         tags:
             - { name: notification.type }