[gtk/kill-containers] Stop using container api on GtkFixed

[Matthias Clasen <matthiasc src gnome org>]

commit 5b88e0c875bc794bce5fd5375c85b6d41992c8b7
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu May 7 15:09:28 2020 -0400

    Stop using container api on GtkFixed
    
    GtkContainer is going away.

 demos/gtk-demo/fixed.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/demos/gtk-demo/fixed.c b/demos/gtk-demo/fixed.c
index dcdf253596..01d792f5be 100644
--- a/demos/gtk-demo/fixed.c
+++ b/demos/gtk-demo/fixed.c
@@ -53,7 +53,7 @@ create_faces (void)
       faces[i].face = gtk_frame_new (NULL);
       gtk_widget_set_size_request (faces[i].face, face_size, face_size);
       gtk_widget_add_css_class (faces[i].face, faces[i].css_class);
-      gtk_container_add (GTK_CONTAINER (fixed), faces[i].face);
+      gtk_fixed_put (GTK_FIXED (fixed), faces[i].face, 0, 0);
 
       /* Set up the transformation for each face */
       transform = gsk_transform_translate (transform, &GRAPHENE_POINT_INIT (w, h));
@@ -139,7 +139,7 @@ create_demo_window (GtkWidget *do_widget)
   gtk_widget_set_valign (GTK_WIDGET (fixed), GTK_ALIGN_CENTER);
 
   cube = create_faces ();
-  gtk_container_add (GTK_CONTAINER (fixed), cube);
+  gtk_fixed_put (GTK_FIXED (fixed), cube, 0, 0);
   gtk_widget_set_overflow (fixed, GTK_OVERFLOW_VISIBLE);
 
   provider = gtk_css_provider_new ();