spark-storage: keepalive test waits on deadlines, not fixed sleeps (intermittent CI failure) - #191

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: peaceiris/actions-mdbook@ee69d230fe19748b7abf22df32acaa93833fad08. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/