chore(AvatarPair): Convert AvatarPair to CSS modules

[jonrohan]

Closes https://github.com/github/primer/issues/4023

I opted in this case to go directly to CSS modules as this component will be removed in the next major release.

Changelog

Changed

Converts AvatarPair to CSS modules

Removed

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

Testing & Reviewing

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• 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]

🦋 Changeset detected

Latest commit: abc9f25

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]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	97.96 KB (-0.03% 🔽)
packages/react/dist/browser.umd.js	98.23 KB (-0.05% 🔽)