[cloud] sns_topic: Fix unreferenced variable

Cherry-pick of 4e759a9cce

CHANGELOG.md

@@ -138,6 +138,8 @@ Ansible Changes By Release
   (https://github.com/ansible/ansible/pull/32203)
 * Fix for validating proxy results on Python3 for modules making http requests:
   (https://github.com/ansible/ansible/pull/32596)
+* Fix unreferenced variable in SNS topic module
+  (https://github.com/ansible/ansible/pull/29117)
 
 
 <a id="2.4.1"></a>

lib/ansible/modules/cloud/amazon/sns_topic.py

@@ -280,7 +280,7 @@ class SnsTopicManager(object):
         for (protocol, endpoint) in desired_subscriptions:
             if (protocol, endpoint) not in subscriptions_existing_list:
                 self.changed = True
-                self.subscriptions_added.append(sub)
+                self.subscriptions_added.append((protocol, endpoint))
                 if not self.check_mode:
                     self.connection.subscribe(self.arn_topic, protocol, endpoint)