执行此操作后：
sudo add-apt-repository ppa:alexlarsson/flatpak
sudo apt update
sudo apt install flatpak
我收到此错误：
E: Your kernels are unsigned. This system will fail to boot in a secure boot environment.
dpkg: error processing package grub-efi-amd64 (--configure):
installed grub-efi-amd64 package post-installation script subprocess returned error exit status 1
dpkg: dependency problems prevent configuration of grub-efi-amd64-signed:
grub-efi-amd64-signed depends on grub-efi-amd64 | grub-pc; however:
Package grub-efi-amd64 is not configured yet.
Package grub-pc is not installed.
dpkg: error processing package grub-efi-amd64-signed (--configure):
dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of shim-signed:
shim-signed depends on grub-efi-amd64-signed; however:
Package grub-efi-amd64-signed is not configured yet.
dpkg: error processing package shim-signed (--configure):
dependency problems - leaving unconfigured
No apport report written because the error message indicates its a followup error from a previous failure.
No apport report written because the error message indicates its a followup error from a previous failure.
Errors were encountered while processing:
grub-efi-amd64
grub-efi-amd64-signed
shim-signed
E: Sub-process /usr/bin/dpkg returned an error code (1)
我认为这是 Ubuntu 18.04 中未签名内核的一个已知错误。flatpack无论如何都能正常工作吗？