Detect if `Husky.install` is used against a worktree inside of `act`

When testing Github workflows locally using `act`, if we use worktrees then running `dotnet husky install` fails because we are not in a real Git repository.

To mitigate the issue, we should detect this scenario, emit a warning and not run `Husky.install`.

We can detect that we are inside of `act` by checking for `ACT` env variables and that we are inside of a worktree by checking that `.git` is actually a file and not a folder.