test: make the Docker harness work on a NixOS host - #52

Unable to download artifact(s): Artifact not found for name: patched-cargo-toml Please ensure that your artifact is not expired and the artifact was uploaded using a compatible version of toolkit/upload-artifact. For more information, visit the GitHub Artifacts FAQ: https://github.com/actions/toolkit/blob/main/packages/artifact/docs/faq.md

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, actions/download-artifact@v4, actions/upload-artifact@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/