AvatarStack: Add keyboard support to `AvatarStack`

[TylerJDev]

Closes https://github.com/github/primer/issues/3348

Changelog

New

• Adds keyboard support to AvatarStack

Changed

Removed

Rollout strategy

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

Testing & Reviewing

Merge checklist

• [x] Added/updated tests
• [ ] Added/updated documentation
• [ ] Added/updated previews (Storybook)
• [ ] Changes are SSR compatible
• [x] Tested in Chrome
• [x] Tested in Firefox
• [x] Tested in Safari
• [ ] Tested in Edge
• [ ] (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 321553adb2bf8489b3a46f5073d1f1eb51e72b22

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Minor

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[github-actions[bot]]

:wave: Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!

[github-actions[bot]]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	97.35 KB (+0.31% 🔺)
packages/react/dist/browser.umd.js	97.59 KB (+0.21% 🔺)

[primer-integration[bot]]

🟢 golden-jobs completed with status success.

[primer-integration[bot]]

:wave: Hi from github/github! Your integration PR is ready: https://github.com/github/github/pull/348018

[TylerJDev]

Requires small changes in Dotcom for tests, https://github.com/github/github/pull/348018/commits/833ad355c270f37218f3bcc4071319846b0e552a. Removes empty space that AvatarStack previously had. More context at https://github.com/github/memex/issues/16409.