Bump phpstan/phpstan from 2.2.7 to 2.2.8 - #116

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, pmmp/setup-php-action@3.2.0. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/