Make stream_change_cache pass no-untyped-defs

mypy.ini

@@ -103,6 +103,9 @@ disallow_untyped_defs = True
 [mypy-synapse.util.caches.dictionary_cache]
 disallow_untyped_defs = True
 
+[mypy-synapse.util.caches.stream_change_cache]
+disallow_untyped_defs = True
+
 [mypy-synapse.util.caches.ttl_cache]
 disallow_untyped_defs = True
 

synapse/util/caches/stream_change_cache.py

@@ -40,10 +40,10 @@ def __init__(
         self,
         name: str,
         current_stream_pos: int,
-        max_size=10000,
+        max_size: int = 10000,
         prefilled_cache: Optional[Mapping[EntityType, int]] = None,
-    ):
-        self._original_max_size = max_size
+    ) -> None:
+        self._original_max_size: int = max_size
         self._max_size = math.floor(max_size)
         self._entity_to_key: Dict[EntityType, int] = {}