tests: Harden subprocess management - #354

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: tim-actions/dco@f2279e6e62d5a7d9115b0cb8e837b777b1b02e21, tim-actions/get-pr-commits@198af03565609bb4ed924d1260247b4881f09e7d. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/