Update sbt, scripted-plugin to 1.12.15 - #213

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830, actions/setup-node@v4, actions/upload-artifact@v5, VirtusLab/scala-cli-setup@68bd9c30954d20e6cb6ddaf01b3b38336f25df4b. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/