build: Add missing test GSchema XML file to dist list
build: Add missing test GSchema XML file to dist list

This was introduced in bug #742997, but not added to the Makefile.am, so
it’s missing from tarballs.

Signed-off-by: Philip Withnall <withnall@endlessm.com>
Reviewed-by: nobody

https://bugzilla.gnome.org/show_bug.cgi?id=792322

endlessm/glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib