DEV: Use consistent interpolation key format in translations

config/locales/client.en.yml

@@ -13,7 +13,7 @@ en:
       cant_act_unclaimed: "You must claim this topic before acting on flags."
       assigned: "Assigned"
       assigned_to: "Assigned to"
-      assign_notification: "<p><span>{{username}}</span> {{description}}</p>"
+      assign_notification: "<p><span>%{username}</span> %{description}</p>"
       unassign:
         title: "Unassign"
         help: "Unassign %{username} from Topic"