bug#29662: 'guix gc' as user makes system unbootable

[Martin Castillo]

I had a similar situation today. guix gc removed the grub background png
from the store. the one, that was used by /boot/grub/grub.cfg. the boot
menu then had a black and blue background. rebuilding the configuration
refetched the background image, but guix gc removed it again.

after rebooting and reconfiguring a few times 'fixed' it. I will report
back, if I should be able to reproduce.

-- 
GPG: 7FDE 7190 2F73 2C50 236E  403D CC13 48F1 E644 08EC