Loupe hard-depends on X11

I found this while trying to build a wayland-only image: gnome-build-meta!454

See:

• https://gitlab.gnome.org/GNOME/loupe/-/blob/main/Cargo.lock?ref_type=heads#L765
• https://gitlab.gnome.org/GNOME/loupe/-/blob/main/Cargo.lock?ref_type=heads#L778