Drop support for PHP 7.x, and PHP 8.0/8.1, new minimum is 8.2. Update PHPUnit to 11. - #166

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