Fix asyncio.wait DeprecationWarning on python 3.9

[leszekhanusz]

Executing the tests with tox on python 3.9 will generate the following DeprecationWarning:

tests/test_async_client_validation.py: 6 tests with warnings
tests/test_phoenix_channel_exceptions.py: 1 test with warning
tests/test_websocket_exceptions.py: 14 tests with warnings
tests/test_websocket_query.py: 2 tests with warnings
tests/test_websocket_subscription.py: 2 tests with warnings
  /home/leszek/git_repos/gql/.tox/py39-dev/lib/python3.9/site-packages/websockets/server.py:712: DeprecationWarning: The explicit passing of coroutine objects to asyncio.wait() is deprecated since Python 3.8, and scheduled for removal in Python 3.11.
    await asyncio.wait(

See Python issue 34790

[leszekhanusz]

This is apparently fixed in websockets master.
See issue websockets #762
We will need to wait for the next release of websockets