Bug#983435: confirmed reproducible

[bugsgrid+deb at gmail.com]

Control: reassign -1 src:grub2
Control: found -1 2.04-10
Control: notfound -1 2.04-9
Control: found -1 2.02+dfsg1-20+deb10u3
Control: notfound -1 2.02+dfsg1-20+deb10u2

Turned out that the symptom was not specific to grub-efi.
It does reproduce on grub-pc too.

Short steps to test:
1) rename /bin/udevadm to something else
2) run grub-install {/dev/sda}
3) make sure no error has happened
4) look, all modules are gone!

thanks very much.