Make it possible to use dmypy (#9692)

Running `dmypy run` will do a `mypy` check while spinning up a daemon
that makes rerunning `dmypy run` a lot faster.

`dmypy` doesn't support `follow_imports = silent` and has
`local_partial_types` enabled, so this PR enables those options and
fixes the issues that were newly raised. Note that `local_partial_types`
will be enabled by default in upcoming mypy releases.

tests/replication/tcp/streams/test_typing.py

@@ -69,6 +69,7 @@ class TypingStreamTestCase(BaseStreamTestCase):
         self.assert_request_is_get_repl_stream_updates(request, "typing")
 
         # The from token should be the token from the last RDATA we got.
+        assert request.args is not None
         self.assertEqual(int(request.args[b"from_token"][0]), token)
 
         self.test_handler.on_rdata.assert_called_once()

tests/replication/test_multi_media_repo.py

@@ -15,7 +15,7 @@
 import logging
 import os
 from binascii import unhexlify
-from typing import Tuple
+from typing import Optional, Tuple
 
 from twisted.internet.protocol import Factory
 from twisted.protocols.tls import TLSMemoryBIOFactory
@@ -32,7 +32,7 @@ from tests.server import FakeChannel, FakeSite, FakeTransport, make_request
 
 logger = logging.getLogger(__name__)
 
-test_server_connection_factory = None
+test_server_connection_factory = None  # type: Optional[TestServerTLSConnectionFactory]
 
 
 class MediaRepoShardTestCase(BaseMultiWorkerStreamTestCase):