Enable nightly build to test 2.15 - #3983

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/github-script@v7, tj-actions/changed-files@d6e91a2266cdb9d62096cebf1e8546899c6aa18f. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/