fix(notifications): post process broadcast notification even without signals

Signed-off-by: Hellgren Heikki <heikki.hellgren@op.fi>

.changeset/wise-suits-protect.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-notifications-backend': patch
+---
+
+Make sure to post process broadcast notifications even without signals support

plugins/notifications-backend/src/service/router.ts

@@ -470,8 +470,8 @@ export async function createRouter(
         },
         channel: 'notifications',
       });
-      postProcessNotification(ret, opts);
     }
+    postProcessNotification(ret, opts);
     return notification;
   };