Bump @primer/octicons from 19.20.0 to 19.21.0 (#933)

Bumps [@primer/octicons](https://github.com/primer/octicons) from 19.20.0 to 19.21.0.
- [Release notes](https://github.com/primer/octicons/releases)
- [Changelog](https://github.com/primer/octicons/blob/main/CHANGELOG.md)
- [Commits](primer/octicons@v19.20.0...v19.21.0)

---
updated-dependencies:
- dependency-name: "@primer/octicons"
  dependency-version: 19.21.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]