Pin GitHub Actions to full-length commit SHAs - #72

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830, actions/checkout@11d5960a326750d5838078e36cf38b85af677262, actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065, actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02, codecov/codecov-action@b9fd7d16f6d7d1b5d2bec1a2887e65ceed900238. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/