build(deps): drop support for Python 3.9 - #323

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: FedericoCarboni/setup-ffmpeg@37062fbf7149fc5578d6c57e08aed62458b375d6. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/