Bump sabberworm/php-css-parser from 8.5.1 to 8.6.0

Bumps [sabberworm/php-css-parser](https://github.com/MyIntervals/PHP-CSS-Parser) from 8.5.1 to 8.6.0.
- [Release notes](https://github.com/MyIntervals/PHP-CSS-Parser/releases)
- [Changelog](https://github.com/MyIntervals/PHP-CSS-Parser/blob/v8.6.0/CHANGELOG.md)
- [Commits](MyIntervals/PHP-CSS-Parser@v8.5.1...v8.6.0)

---
updated-dependencies:
- dependency-name: sabberworm/php-css-parser
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

composer.json

@@ -17,7 +17,7 @@
     "ampproject/amp-toolbox": "0.11.5",
     "cweagans/composer-patches": "^1.0",
     "fasterimage/fasterimage": "1.5.0",
-    "sabberworm/php-css-parser": "8.5.1"
+    "sabberworm/php-css-parser": "8.6.0"
   },
   "require-dev": {
     "automattic/vipwpcs": "^3.0",