Port tests/ to Python 3 (#3808)

changelog.d/3808.misc

tests/api/test_auth.py

tests/app/test_frontend_proxy.py

tests/handlers/test_typing.py

tests/rest/client/v1/test_rooms.py

tests/rest/client/v2_alpha/test_sync.py

tests/server.py

tests/server_notices/test_resource_limits_server_notices.py

tests/storage/test_state.py

tests/test_mau.py

tests/test_state.py

tests/utils.py