fix(ui-radio-input): set aria-required on RadioInputGroup when isRequired

[balzss]

Summary

• RadioInputGroup v2 sets aria-required on the role="radiogroup" element when isRequired is true, so screen readers announce the group as required.
• Updated the isRequired prop doc and the README "Required Fields" section.
• v2 only. Setting the native required attribute is not part of this change, it is tracked in INSTUI-5187.

Test Plan

• With a screen reader, move focus into a RadioInputGroup that has isRequired and confirm the group is announced as required.
• Confirm form submission is still not blocked when no option is selected.

Fixes INSTUI-5186

[github-actions]

PR Preview Action v1.8.1
🚀 View preview at https://instructure.design/pr-preview/pr-2716/
Built to branch gh-pages at 2026-09-11 09:48 UTC. Preview will be ready when the GitHub Pages deployment is complete.

[github-actions]

Visual regression report

Cypress suite: ✅ Passing

Visual diff: ⚠️ Changes detected.

Status	Count
Unchanged	94
Changed	2
New	0
Removed	0

Accessibility (axe): ✅ No violations.

📊 View full report — click a screenshot's ⚠ badge to see each violation boxed on the image, with the offending element named and contrast failures shown as color swatches.

Diff images (2)

tooltip-dark.png — 881 pixels differ

tooltip-light.png — 956 pixels differ

_{Baselines come from the visual-baselines branch. They refresh on every merge to master. The Cypress suite line covers the a11y and console-error assertions — a ❌ there means the suite found real issues even if the visual diff is clean.}

[matyasf]

Works well in Vo and NVDA, but I did not get the 'required' announcement in JAWS + Chrome. I think its OK?

[balzss]

Works well in Vo and NVDA, but I did not get the 'required' announcement in JAWS + Chrome. I think its OK?

considering that the a11y audit didn't even flag the previous version, i think it's ok and still a good upgrade