RuntimeError in aiohttp's TimerContext with 0.11.0

[ods]

Minimal example to reproduce:

from aiohttp.client import ClientSession
import pytest


@pytest.fixture
async def session():
    session = ClientSession()
    yield session
    await session.close()


@pytest.mark.asyncio
async def test_aiohttp(session):
    async with session.get('http://example.com/') as response:
        pass

The test output:

============================================= FAILURES =============================================
___________________________________________ test_aiohttp ___________________________________________
Traceback (most recent call last):
  File "/usr/src/tests/test_aiohttp.py", line 16, in test_aiohttp
    async with session.get('http://example.com/') as response:
  File "/usr/local/lib/python3.7/site-packages/aiohttp/client.py", line 1012, in __aenter__
    self._resp = await self._coro
  File "/usr/local/lib/python3.7/site-packages/aiohttp/client.py", line 426, in _request
    with timer:
  File "/usr/local/lib/python3.7/site-packages/aiohttp/helpers.py", line 579, in __enter__
    raise RuntimeError('Timeout context manager should be used '
RuntimeError: Timeout context manager should be used inside a task
===================================== short test summary info ======================================
FAILED tests/test_aiohttp.py::test_aiohttp - RuntimeError: Timeout context manager should be used...
======================================== 1 failed in 0.17s =========================================

Works fine with 0.10.0 or when session is created directly in the test instead of fixture.

[simonfagerholm]

Same root cause as #154 and #157, tested the example with #156 and it works.