bug#65770: xdg-desktop-portal-kde only works if system is reconfigured with gnome-desktop-service-type

[Nathan Dehnel]

if gnome-desktop is enabled:
-kde file picker works
if gnome-dekstop is not installed:
Gtk-WARNING **: 22:04:20.326: Can't open portal file chooser:
GDBus.Error:org.freedesktop.DBus.Error.Spawn.ChildSignaled: Process
org.freedesktop.portal.Desktop received signal 5

guix c3d48d0