ci: run the unit tests on every push and pull request - #55

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, actions/setup-node@v2, docker/build-push-action@v4, docker/login-action@v2. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/