fix(process): reap entire process group on cmd.Cancel - #39143

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: denoland/setup-deno@11b63cf76cfcafb4e43f97b6cad24d8e8438f62d. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/