Fix hera plan-DAG hygiene: orphaned planned nodes + silent materialize retry - #914

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: tj-actions/changed-files@aa08304bd477b800d468db44fe10f6c61f7f7b11. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/