winproto/wayland: disable custom blur on GTK >=4.23.3

GTK 4.23.3 added its own (much smarter) implementation of background blur,
which means our implementation is not only redundant, it also crashes the
program because a surface cannot have multiple associated blur objects.
Ergo, don't do custom blur on newer GTK versions.

See #13578

src/apprt/gtk/winproto/wayland.zig

@@ -174,6 +174,12 @@ pub const Window = struct {
         };
 
         const bg_effect: ?*ext.BackgroundEffectSurfaceV1 = bg: {
+            if (gtk_version.runtimeAtLeast(4, 23, 3)) {
+                // GTK 4.23.3 added an official way to do background blur,
+                // so we don't need to do anything on our own.
+                break :bg null;
+            }
+
             const mgr = app.globals.get(.ext_background_effect) orelse
                 break :bg null;