Bump @primer/css from 20.8.1 to 21.0.8 (#357)

Bumps [@primer/css](https://github.com/primer/css) from 20.8.1 to 21.0.8.
- [Release notes](https://github.com/primer/css/releases)
- [Changelog](https://github.com/primer/css/blob/main/CHANGELOG.md)
- [Commits](primer/css@v20.8.1...v21.0.8)

---
updated-dependencies:
- dependency-name: "@primer/css"
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

package.json

@@ -41,7 +41,7 @@
     "@changesets/changelog-github": "0.4.7",
     "@changesets/cli": "2.26.1",
     "@github/prettier-config": "0.0.6",
-    "@primer/css": "^20.0.0",
+    "@primer/css": "^21.0.8",
     "@primer/primitives": "^7.11.11",
     "dedent": "0.7.0",
     "eslint": "8.39.0",