wayland: Set type for GtkSelectionData for incoming contents

This is set from the incoming property type under X11.  Under Wayland
it will always be what we requested, so we can just set it to the target.

gtk/gtkclipboard-wayland.c

@@ -247,6 +247,7 @@ _request_generic_cb (GdkDevice   *device,
 
   selection_data.selection = GDK_SELECTION_CLIPBOARD;
   selection_data.target = closure->target;
+  selection_data.type = closure->target;
   selection_data.length = len;
   selection_data.data = (guchar *)data;