get_client test warnings / tests skipped

[jreiberkyle]

Expected behavior
running nox would result in no warnings and all tests would be run

Actual behavior (describe the problem)
running nox results in the following output from the test sessions:

============================================== warnings summary ===============================================
tests/unit/test_session.py::test_session_get_client[data-DataClient]
tests/unit/test_session.py::test_session_get_client[orders-OrdersClient]
tests/unit/test_session.py::test_session_get_client[subscriptions-SubscriptionsClient]
tests/unit/test_session.py::test_session_get_client_error
  /Users/jennifer.kyle/pl/planet-client-python/.nox/test-3-7/lib/python3.7/site-packages/_pytest/python.py:184: PytestUnhandledCoroutineWarning: async def functions are not natively supported and have been skipped.
  You need to install a suitable plugin for your async framework, for example:
    - anyio
    - pytest-asyncio
    - pytest-tornasync
    - pytest-trio
    - pytest-twisted
    warnings.warn(PytestUnhandledCoroutineWarning(msg.format(nodeid)))

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=========================================== short test summary info ===========================================
SKIPPED [4] .nox/test-3-7/lib/python3.7/site-packages/_pytest/python.py:185: async def function and no async plugin installed (see warnings)
================================= 490 passed, 4 skipped, 4 warnings in 4.47s ==================================

Installation Method
pip install -e . on latest in main branch

[kevinlacaille]

Closed by #881