chore(typing): Try MonkeyType on modules in responses codebase (#616)

responses/__init__.py

@@ -674,7 +674,7 @@ def __init__(
         passthru_prefixes: Tuple[str, ...] = (),
         target: str = "requests.adapters.HTTPAdapter.send",
         registry: Type[FirstMatchRegistry] = FirstMatchRegistry,
-    ):
+    ) -> None:
         self._calls: CallList = CallList()
         self.reset()
         self._registry: FirstMatchRegistry = registry()  # call only after reset