error: cannot lock ref 'refs/remotes/origin/master': is at xxxx

[annatagus]

multi-magit invokes commands in parallel and that is problematic when both a main repo and one or more of its worktrees are selected.

[luismbo]

We could start by making these commands run in sequence (make it correct) and then perhaps detect which repos can be manipulated in parallel (make it fast). For some operations, we can always run in parallel if the command is read-only.