ContextVars are not propagated from fixtures with pytest-asyncio

[pgjones]

This is more of a pytest-asyncio bug, see pytest-dev/pytest-asyncio#127

@pytest.fixture(scope='class')
async def test_context(self):
    async with app.app_context():
        async with app.test_request_context("/"):
            setattr(quart.g, 'test', 'value')
            yield

@pytest.mark.asyncio
async def test_global(test_context):
    assert quart.g.test == 'value'