In Nixpkgs packages are installed in separate prefixes.
Starting from GLib / gobject-introspection 2.80, GLib introspection data
is provided by GLib itself instead of gobject-introspection. This causes
tests failures in Nixpkgs because the GI_TYPELIB_PATH set by the build
environment was overridden, leaving it unable to find GLib:
ImportError: cannot import name GLib, introspection typelib not found
Only GI_TYPELIB_PATH needs to be preserved in our case, but I've made
the same change for LD_LIBRARY_PATH, other environments might rely on
that in a similar way.