feat: add docker environment to run the checks locally - #57

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: shivammathur/setup-php@7bf05c6b704e0b9bfee22300130a31b5ea68d593. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/