Merge branch 'fix-virtual-memory-leak' into 'gtk-3-24'

Ensure the staging_cairo_surface is destroyed before re-assigning it

See merge request GNOME/gtk!7206

gdk/wayland/gdkwindow-wayland.c

@@ -954,6 +954,7 @@ buffer_release_callback (void             *_data,
   /* Release came in, we haven't done any interim updates, so we can just use
    * the old committed buffer again.
    */
+  g_clear_pointer (&impl->staging_cairo_surface, cairo_surface_destroy);
   impl->staging_cairo_surface = g_steal_pointer (&impl->committed_cairo_surface);
 }