Bump postcss from 8.4.38 to 8.5.10 in /site

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.38 to 8.5.10.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.38...8.5.10)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.10
  dependency-type: direct:development
...

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

Author: dependabot[bot]

site/package.json

@@ -93,7 +93,7 @@
     "lint-staged": "^15.2.2",
     "lunr": "^2.3.9",
     "npm-run-all": "^4.1.5",
-    "postcss": "^8.4.38",
+    "postcss": "^8.5.10",
     "postcss-html": "^1.7.0",
     "prettier": "^3.2.5",
     "prettier-plugin-astro": "^0.13.0",