Bump @primer/css from 12.3.1 to 12.6.0

Bumps [@primer/css](https://github.com/primer/css) from 12.3.1 to 12.6.0.
- [Release notes](https://github.com/primer/css/releases)
- [Changelog](https://github.com/primer/css/blob/master/CHANGELOG.md)
- [Commits](https://github.com/primer/css/compare/v12.3.1...v12.6.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -11,7 +11,7 @@
     "stylelint-selector-no-utility": "^4.0.0"
   },
   "dependencies": {
-    "@primer/css": "^12.3.1"
+    "@primer/css": "^12.6.0"
   },
   "scripts": {
     "test": "stylelint '**/*.scss'"