Merge branch 'bf/set-head-symref'

When "git fetch $remote" notices that refs/remotes/$remote/HEAD is missing and discovers what branch the other side points with its HEAD, refs/remotes/$remote/HEAD is updated to point to it. * bf/set-head-symref: fetch set_head: handle mirrored bare repositories fetch: set remote/HEAD if it does not exist refs: add create_only option to refs_update_symref_extended refs: add TRANSACTION_CREATE_EXISTS error remote set-head: better output for --auto remote set-head: refactor for readability refs: atomically record overwritten ref in update_symref refs: standardize output of refs_read_symbolic_ref t/t5505-remote: test failure of set-head t/t5505-remote: set default branch to main