Switch CI from ponyc nightly back to release - #75

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: andymckay/labeler@467347716a3bdbca7f277cb6cd5fa9c5205c5412. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/