Pin Ruff version - #83

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v3.3.0, codecov/codecov-action@v4.0.1. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Codecov: Failed to properly create commit: The process '/__w/_actions/codecov/codecov-action/v4.0.1/dist/codecov' failed with exit code 1

Codecov: Error importing pgp key