[Gtk] Fix gtk_label_get string to be out param.

Author: Therzok

gtk/Gtk.metadata

@@ -936,4 +936,5 @@
   <attr path="/api/namespace/object[@cname='GtkIconView']/method[@cname='gtk_icon_view_get_tooltip_context']/parameters/parameter[@name='path']" name="owned">true</attr>
   <attr path="/api/namespace/object[@cname='GtkTreeView']/method[@cname='gtk_tree_view_get_tooltip_context']/parameters/parameter[@name='path']" name="owned">true</attr>
   <attr path="/api/namespace/class[@cname='GtkGlobal']/method[@cname='gtk_parse_args']" name="hidden">1</attr>
+  <attr path="/api/namespace/object[@cname='GtkLabel']/method[@cname='gtk_label_get']/parameters/parameter[@name='str']" name="pass_as">out</attr>
 </metadata>