push_notifications: Give full stack information on an exception.

This error has been seen in production instances, but we need more
context to be able to determine what might be causing it.

zerver/lib/push_notifications.py

@@ -893,6 +893,7 @@ def handle_push_notification(user_profile_id: int, missed_message: Dict[str, Any
                 "Could not find UserMessage with message_id %s and user_id %s",
                 missed_message["message_id"],
                 user_profile_id,
+                exc_info=True,
             )
             return
 

zerver/tests/test_push_notifications.py

@@ -1176,6 +1176,7 @@ class HandlePushNotificationTest(PushNotificationTest):
                 "Could not find UserMessage with message_id %s and user_id %s",
                 message_id,
                 self.user_profile.id,
+                exc_info=True,
             )
             mock_push_notifications.assert_called_once()