feat: add git worktree isolation via port shifting - #421

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: castor-php/setup-castor@827c7ae1be0bb45e42a6082cad943a2afe0ffd40. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/