Bump CI to Python 3.11 and upgrade filelock to 4.2.9 - #78

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/upload-artifact@v4, tj-actions/changed-files@v46.0.5. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/