ci(release): check_release.sh / prepare_beta.sh; version-bump keeps betas; release branches checked in CI (#1498) - #1709

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