gnome-initial-setup: disable software-sources

We do not have packagekit in the repository, upon which this
feature depends. It seems to complain at least on my system, so
disable it explicitly.

srcpkgs/gnome-initial-setup/template

@@ -3,6 +3,7 @@ pkgname=gnome-initial-setup
 version=3.30.0
 revision=1
 build_style=meson
+configure_args="-Dsoftware-sources=disabled"
 hostmakedepends="pkg-config glib-devel"
 makedepends="NetworkManager-devel accountsservice-devel libglib-devel
  gnome-desktop-devel cheese-devel libgweather-devel webkit2gtk-devel