docs: fix TC18.txt citation drift in discovery.rs/request.rs + mdio.rs:130 (issue #164 batch 3) - #167

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, rustsec/audit-check@v1. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/