This is because wlroots has migrated to gitlab and the github repo has been archived. The guix wlroots package still uses the github repo as you can see on line 1546 of ./gnu/packages/wm.scm.

Since hyprland is made to be built with the latest wlroots version it fails to build with the old github version. Possible solutions would be to use the bundled wlroots or update the wlroots package in wm.scm to the new source.

 

I would send a patch if I could but I'm not familiar enough with guix and guile to do so.