Bump primer/css

[camertron]

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Please read this description carefully. If you feel there is anything unclear or missing, please ask for updates.

What are you trying to accomplish?

This PR bumps primer/css to the latest version to take advantage of the fact that the latest version no longer depends on primer/view-components and therefore leads to fewer version conflicts in GitHub's main monorepo.

Integration

Production apps will need to upgrade to primer/css v21.5.0.

Risk Assessment

• Low risk the change is small, highly observable, and easily rolled back.
• Medium risk changes that are isolated, reduced in scope or could impact few users. The change will not impact library availability.
• High risk changes are those that could impact customers and SLOs, low or no test coverage, low observability, or slow to rollback.

Accessibility

• No new axe scan violation - This change does not introduce any new axe scan violations.

Merge checklist

• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

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[changeset-bot]

🦋 Changeset detected

Latest commit: 58ce519

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

This PR includes changesets to release 1 package

Name	Type
@primer/view-components	Minor

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