gdbus-exit-on-close test: don't leak a variant

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=662100
Bug-NB: NB#287088
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Reviewed-by: Colin Walters <walters@verbum.org>

gio/tests/gdbus-exit-on-close.c

@@ -167,6 +167,7 @@ test_exit_on_close (gconstpointer test_data)
                                            &error);
           g_assert_no_error (error);
           g_assert (v != NULL);
+          g_variant_unref (v);
 
           g_dbus_connection_close (c, NULL, close_async_cb, NULL);
         }