Correct PRODUCT_RELEASE behaviour and document RELEASE_INCLUDES - #164

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4, actions/checkout@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Summary report available at: https://github.com/sbomify/sbomify.com/actions/runs/40394304622#summary-121823141835