Fix spot spectra for stars with spots - #265

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/