no-aria-label should ignore decorative SVG with aria-hidden=true (bis)

[PhilippeVay]

#472 but better...

Closes #387

An SVG with aria-hidden=true is decorative, no need to check for aria-label or aria-labelledby.

Done:

1. in errors.scss rule no-aria-label, adding :not([aria-hidden=true]) to each selector
2. re-build CSS files
3. update documentation

Proposed new description is:

[role=img] without [aria-hidden=true] should either have [aria-label] or [aria-labelledby].
If image is decorative, please use [role=presentation] instead.

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[ffoodd]

Thanks for this, this is nicely done! ❤️

I'm going with it, but as a sidenote for future reader: you're not supposed to use role="img" on a decorative SVG. Either use aria-hiden="true" or role="presentation".