chore(deps-dev): bump postcss from 8.5.10 to 8.5.18 (#455)

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.10 to 8.5.18.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.5.10...8.5.18)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.18
  dependency-type: direct:development
...

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sites/promo/package.json

@@ -35,7 +35,7 @@
     "@types/react-dom": "^19",
     "eslint": "^9",
     "eslint-config-next": "15.4.4",
-    "postcss": "^8.5.6",
+    "postcss": "^8.5.18",
     "prettier": "^3.6.2",
     "prettier-plugin-organize-imports": "^4.2.0",
     "prettier-plugin-tailwindcss": "^0.6.14",