Comment 6 for bug 1825128

per code in ubiquity:/usr/share/grub-installer/grub-installer
it install grub-efi-amd64-signed first, and then install shim-signed.
(grub_package=grub-efi-amd64-signed as the code run to here.)
===
        apt-install $grub_package || exit_code=$?
        case $grub_package in
            *-signed)
                apt-install shim-signed || true
                apt-install grub-pc || true
                ;;
        esac
===