Add remaining type hints to synapse.events.

synapse/events/__init__.py

@@ -352,8 +352,8 @@ def get_templated_pdu_json(self) -> JsonDict:
 
         return template_json
 
-    def __set__(self, instance: Any, value: Any) -> None:
-        raise AttributeError("Unrecognized attribute %s" % (instance,))
+    def __setattr__(self, key: str, value: Any) -> None:
+        raise AttributeError("Unrecognized attribute %s" % (key,))
 
     def __getitem__(self, field: str) -> Optional[Any]:
         return self._dict[field]