bug#50676: [core-updates-frozen] Image production is broken.

[Mathieu Othacehe]

Hey,

The duplicated system derivation appears to be a grafted version of
the first one.

Running:

--8<---------------cut here---------------start------------->8---
./pre-inst-env guix system image gnu/system/examples/bare-bones.tmpl -t qcow2 
--no-grafts
--8<---------------cut here---------------end--------------->8---

produces an image that boots fine in QEMU.

Mathieu