aria-required attribute on input[type="radio"] is invalid in ARIA

Problem/Motivation

ARIA 1.1 specifies that the aria-required attribute isn't allowed on an element with role="radio"--including an input with a radio type. aria-required is allowed on a radiogroup role (which would be <fieldset> in this case), but not on the inputs themselves. This was confirmed by Wilco Fiers that aria-required wasn't intended to be allowed on the radio role.

This markup causes some accessibility checks to fail pages with webforms containing required radio elements.

Steps to reproduce

1. Install local Drupal 9 and latest version of Webform (6.0.3 as of ticket's creation date)
2. Create a new webform, or use default Contact form
3. Add a radio element (use any custom value setting for inputs, I chose gender option for radio)
4. Rendered markup shows inputs with type of radio have aria-required="true"

Proposed resolutions

1. Preferred: Remove the aria-required attribute from the rendered tag, using only the required attribute instead.
2. Backup solution: If the idea is to convey the grouping of radio inputs is required (not the individual inputs), the fieldset may allow an aria-required="true" value, so the required state could be applied to the grouping instead of the inputs themselves. Support at the time seemed spotty, but in a quick Codepen test announced as expected in VoiceOver/Safari on macOS Catalina. Needs more testing to confirm this works in other combos.

User interface changes

Shouldn't be any user interface changes.