fix: build and typecheck with postcss 8.5 - #1516

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5, jayu/super-labeler-action@e0d24c761fc20458dafd9f3951698e94b1822657. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/