Fix iteration over pubsub list

The iteration deleted from the list as it iterated, causing an item to
be skipped over (and potentially other undefined behaviour).

fakenewsredis.py

@@ -1675,7 +1675,7 @@ def publish(self, channel, message):
         ``message`` to them for the given ``channel``.
         """
         count = 0
-        for i, ps in enumerate(self._pubsubs):
+        for i, ps in list(enumerate(self._pubsubs)):
             if not ps.subscribed:
                 del self._pubsubs[i]
                 continue