Bump dependencies (#874)

* fix pytest-asynio bump to 0.19

* bump mypy

* fix coverage of async fixtures

tests/test_deferred/test_forward_refs.py

@@ -3,6 +3,7 @@ from typing import List
 
 import databases
 import pytest
+import pytest_asyncio
 import sqlalchemy as sa
 from pydantic.typing import ForwardRef
 from sqlalchemy import create_engine
@@ -77,7 +78,7 @@ def create_test_database():
     metadata.drop_all(engine)
 
 
-@pytest.fixture(scope="function")
+@pytest_asyncio.fixture(scope="function")
 async def cleanup():
     yield
     async with db: