Update postcss to 8.5.28 [SECURITY] - #2740

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: github/codeql-action/analyze@9e8d0789d4a0fa9ceb6b1738f7e269594bdd67f0, github/codeql-action/init@9e8d0789d4a0fa9ceb6b1738f7e269594bdd67f0. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/