Confirm this bug. I think it was introduced when upgrading to debhelper compat 12 in 6.0.0-1; dh_installsystemduser was added to the default sequence at this level anyway.
For now I'll make it just install the unit and not auto-enable it, then the user can selectively enable it if desired. That was the intended behaviour. (The gdm copy can be disabled with `systemctl --user --global disable jupyter-notebook`)
