Merge branch 'sj/ref-consistency-checks-more'

"git fsck" becomes more careful when checking the refs. * sj/ref-consistency-checks-more: builtin/fsck: add `git refs verify` child process packed-backend: check whether the "packed-refs" is sorted packed-backend: add "packed-refs" entry consistency check packed-backend: check whether the refname contains NUL characters packed-backend: add "packed-refs" header consistency check packed-backend: check if header starts with "# pack-refs with: " packed-backend: check whether the "packed-refs" is regular file builtin/refs: get worktrees without reading head information t0602: use subshell to ensure working directory unchanged