Merge branch 'dk/worktree-dup-checkout-with-bare-is-ok'

In a worktree connected to a repository elsewhere, created via "git worktree", "git checkout" attempts to protect users from confusion by refusing to check out a branch that is already checked out in another worktree. However, this also prevented checking out a branch, which is designated as the primary branch of a bare reopsitory, in a worktree that is connected to the bare repository. The check has been corrected to allow it. * dk/worktree-dup-checkout-with-bare-is-ok: worktree: allow the main brach of a bare repository to be checked out