Merge branch 'ky/branch-m-worktree' into maint

When "git worktree" feature is in use, "git branch -m" renamed a branch that is checked out in another worktree without adjusting the HEAD symbolic ref for the worktree. * ky/branch-m-worktree: set_worktree_head_symref(): fix error message branch -m: update all per-worktree HEADs refs: add a new function set_worktree_head_symref