fix https://github.com/QubesOS/qubes-issues/issues/5733
Going a bit further, and removing the previous instructions:
~~~
sudo mkdir -p /boot/grub
sudo apt install --no-install-recommends linux-image-amd64 linux-headers-amd64 grub2-common qubes-kernel-vm-support
sudo update-grub
~~~
The directory "/boot/grub/" already exist on the "Debian Template", and will be created by "grub2" if it doesn't exist (like for the "Debian Minimal Template").
Tested the modification on a qube based on Debian Template, and on a qube based on Debian Minimal Template. Both seems to work correctly.
