docs: ensure announcement is made on dynamic content

[khiga8]

Fixes: https://github.com/github/accessibility-audits/issues/10031

Changed

Adds the announceOnShow attribute to the AlertStatus to ensure that polite announcements happen when the component is shown

Side note: I noticed these announcement components don't have a corresponding Primer docs page or guidance on how to use. Is that intentional? happy to follow up here separately.

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Merge checklist

• Added/updated previews (Storybook)

[changeset-bot]

⚠️ No Changeset found

Latest commit: 1359cd7

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[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	104.22 KB (0%)
packages/react/dist/browser.umd.js	104.58 KB (0%)

[khiga8]

superceded by #5568