Bump @primer/css from 19.4.0 to 20.2.3

Bumps [@primer/css](https://github.com/primer/css) from 19.4.0 to 20.2.3.
- [Release notes](https://github.com/primer/css/releases)
- [Changelog](https://github.com/primer/css/blob/main/CHANGELOG.md)
- [Commits](primer/css@v19.4.0...v20.2.3)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

package-lock.json

@@ -10,7 +10,7 @@
   ],
   "dependencies": {
     "@github/failbot": "0.8.0",
-    "@primer/css": "^19.8.2",
+    "@primer/css": "^20.2.3",
     "@primer/octicons": "17.3.0",
     "@primer/octicons-react": "17.3.0",
     "@primer/react": "^34.7.1",