Add scrollbar-gutter prop to PageLayoutPane

[dipree]

Without scrollbar-gutter (or set to auto)

https://github.com/primer/react/assets/3369400/529c8f19-5ad3-46c6-a25b-6099488db6db

Set to scrollbar-gutter: stable

https://github.com/primer/react/assets/3369400/94c20058-472e-466e-9770-6d07e614d0b7

https://developer.mozilla.org/en-US/docs/Web/CSS/scrollbar-gutter

Changelog

New

Changed

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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[bot]]

⚠️ No Changeset found

Latest commit: 70ef9ac970a3b332e06ee69f29678514dc0307da

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[github-actions[bot]]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	88.36 KB (+0.02% 🔺)
packages/react/dist/browser.umd.js	88.6 KB (-0.05% 🔽)

[github-actions[bot]]

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