Move Heading component to staff feature flag

[jonrohan]

Closes https://github.com/github/primer/issues/3716

Heading has been team shipped for a week without any issues, promoting to staff ship based on lifecycle. https://github.com/github/primer-engineering/discussions/138

Changelog

Changed

Heading CSS modules behind primer_react_css_modules_staff feature flag.

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 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)

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🦋 Changeset detected

Latest commit: 5228c9f

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	Patch

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[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	96.42 KB (+0.05% 🔺)
packages/react/dist/browser.umd.js	96.76 KB (+0.05% 🔺)