Avoid require pytest-asyncio CLI args/config if not running visual regression tests #45
Description
@martinRenou Other than dropping Py3.6 support and adding it to the config file, is there any way to avoid requiring the --asyncio-mode=auto CLI arg (and the dependency) every time we run tests, even if we don't run the visual regression tests?
On top of that, there seems to be a bug where running pytest --help, even with --asyncio-mode=auto, displays the error every time unless the config file is manually edited to include it. This probably should be reported somewhere upstream, but in the meantime it isn't so nice for potential new contributors to not even be able to run pytest --help without knowing the magic flag to add.
If this is not possible until we drop Py3.6 (planned for 0.3.0), I'll add an explicit prominent mention of this to the contributing guide and perhaps the readme too.