From a worktree shouldn't be allow to attempt to switch to a branch checked out on the default worktree

[eamodio]

Steps:

1. Have a branch (e.g. main) checked out on the default worktree
2. Open a different worktree
3. Attempt to switch to main from that worktree
4. 🐛 It will give you the following error:

Instead we should not allow you to attempt to switch to that branch.