Allow git commands in git worktrees

The guide currently suggests using [git worktrees](https://ubuntu.com/workshop/docs/how-to/develop-with-workshops/use-git/#use-worktrees) to spawn a separated workshop. This is incredibly useful with AI agents as you can run them in `yolo` mode inside a workshop.

However, any `git` command fails as the worktrees folders symlink to the "main" folder which clearly isn't mounted in the workshop. As such, things like running github actions, AI reviews and in general anything git-related stops working.

Start with the linked workshop guide section on using git worktrees, then reproduce a failing git command from a worktree inside a workshop. Trace how worktree folders are mounted or symlinked to the main folder; done means git commands, including GitHub Actions or AI review workflows, work from the separated workshop.

Written by the indexing model from the issue text.