Fix carousels' improper aria-roledescription

[corinagum]

Fixes #3537

Changelog Entry

• Fixes #3537. Fix some carousels improperly using aria-roledescription, by @corinagum in PR #3599

Description

Fix roles in carousels

Specific Changes

• Adds role to activity message bubble in carousels
• Fixes incorrect role for <li> (group ⇒ listitem)

• I have added tests and executed them locally
• I have updated CHANGELOG.md
• I have updated documentation

Review Checklist

This section is for contributors to review your work.

• Accessibility reviewed (tab order, content readability, alt text, color contrast)
• Browser and platform compatibilities reviewed
• CSS styles reviewed (minimal rules, no z-index)
• Documents reviewed (docs, samples, live demo)
• Internationalization reviewed (strings, unit formatting)
• package.json and package-lock.json reviewed
• Security reviewed (no data URIs, check for nonce leak)
• Tests reviewed (coverage, legitimacy)