Merge branch 'jk/init-core-worktree-at-root' into maint

We avoid setting core.worktree when the repository location is the ".git" directory directly at the top level of the working tree, but the code misdetected the case in which the working tree is at the root level of the filesystem (which arguably is a silly thing to do, but still valid). * jk/init-core-worktree-at-root: init: don't set core.worktree when initializing /.git