Type hints for tests.appservice (#14990)

* Accept a Sequence of events in synapse.appservice

This avoids some casts/ignores in the tests I'm about to fixup. It seems
that `List[Mock]` is not a subtype of `List[EventBase]`, but
`Sequence[Mock]` is a subtype of `Sequence[EventBase]`. So presumably
`Mock` is considered a subtype of anything, much like `Any`.

* make tests.appservice.test_scheduler pass mypy

* Extra hints in tests.appservice.test_scheduler

* Extra hints in tests.appservice.test_api

* Extra hints in tests.appservice.test_appservice

* Disallow untyped defs

* Changelog

synapse/appservice/scheduler.py

@@ -57,6 +57,7 @@ from typing import (
     Iterable,
     List,
     Optional,
+    Sequence,
     Set,
     Tuple,
 )
@@ -364,7 +365,7 @@ class _TransactionController:
     async def send(
         self,
         service: ApplicationService,
-        events: List[EventBase],
+        events: Sequence[EventBase],
         ephemeral: Optional[List[JsonDict]] = None,
         to_device_messages: Optional[List[JsonDict]] = None,
         one_time_keys_count: Optional[TransactionOneTimeKeysCount] = None,