Remove Banner from experimental

[pksjce]

Closes #https://github.com/github/primer/issues/5628

Changelog

Once this https://github.com/github/github-ui/pull/2576 gets merged, we won't have any more references for Banner from @primer/react/experimental

New

Changed

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: 9d28ef6

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

This PR includes changesets to release 2 packages

Name	Type
@primer/react	Major
@primer/styled-react	Major

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[Copilot]

Pull Request Overview

This PR removes the Banner component from the experimental exports, moving it from experimental to stable API status. This is part of the component's graduation process once external references are cleaned up.

• Removes Banner and BannerProps exports from the experimental index
• Updates test snapshots to reflect the removed experimental exports

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/react/src/experimental/index.ts	Removes Banner component and type exports from experimental namespace
packages/react/src/tests/snapshots/exports.test.ts.snap	Updates snapshot to reflect removal of Banner from experimental exports

[github-actions]

👋 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!

[pksjce]

We have zero instances of Banner from @primer/react/experimental on github-ui 👍 This one is also ready to merge