FIX: the notification data on the client expects an identifier (#18850)

plugins/chat/app/jobs/regular/chat_notify_mentioned.rb

@@ -51,6 +51,7 @@ module Jobs
       when :global_mentions
         data[:identifier] = "all"
       else
+        data[:identifier] = identifier_type if identifier_type
         data[:is_group_mention] = true
       end
 

plugins/chat/spec/jobs/regular/chat_notify_mentioned_spec.rb

@@ -445,7 +445,7 @@ describe Jobs::ChatNotifyMentioned do
           track_core_notification(message: message, to_notify_ids_map: to_notify_ids_map)
         data_hash = created_notification.data_hash
 
-        expect(data_hash[:identifier]).to be_nil
+        expect(data_hash[:identifier]).to eq(@chat_group.name)
         expect(data_hash[:is_group_mention]).to eq(true)
       end