Check for `role=figure` instead of `role=group` for figures

[ffoodd]

Hi. I greatly value a11y.css as a tool for quick assessment, but this warning about role="group" throws me off every time...

There is an open ticket on the referenced WAI Tutorial repo indicating that, as of 2017, ARIA 1.1 provides role="figure". Since this is the implicit ARIA role of the <figure> tag, shouldn't this be the correct role to assign, rather than overriding it with group? An investigation by Scott O'Hara and his markup recommendation seem to support that as well: https://www.scottohara.me/blog/2019/01/21/how-do-you-figure.html

PS: I summarized my "research" on the issue on my blog.

Originally posted by @sebastiangreger in https://github.com/ffoodd/a11y.css/issues/121#issuecomment-671073352