Use create_task when calling _read_stream during test_utils

[muellerzr]

Gets rid of:

================================================================ warnings summary =================================================================
tests/test_cli.py::AccelerateLauncherTester::test_config_compatibility
tests/test_cli.py::AccelerateLauncherTester::test_config_compatibility
tests/test_cli.py::AccelerateLauncherTester::test_config_compatibility
tests/test_cli.py::AccelerateLauncherTester::test_no_config
  /home/zach/accelerate/accelerate/src/accelerate/test_utils/testing.py:339: 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(

when running tests on py 3.9

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[sgugger]

LGTM!