Backport !1111 “gs-install-appstream: add gs_private_libdir to rpath” to gnome-41
requested to merge pwithnall/gnome-software:backport-1111-install-appstream-libdir-gnome-41 into gnome-41
This avoids a crash where the executable crashed due to not being able to load the library
Trivial backport of !1111 (merged) to gnome-41.