build.rs: replace manual Option::filter with .filter() - #1667

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: ./.github/actions/install-rust, actions/checkout@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/