[gtk/wip/chergert/macos-iosurface] add missing include dropped from patch

[Christian Hergert <chergert src gnome org>]

commit fce5fd12c1a0144b04c1fc89e403d06524c998ca
Author: Christian Hergert <christian hergert me>
Date:   Wed Feb 9 14:28:55 2022 -0800

    add missing include dropped from patch

 gdk/macos/GdkMacosTile.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gdk/macos/GdkMacosTile.c b/gdk/macos/GdkMacosTile.c
index dd7c84b95d..3c9eaf171f 100644
--- a/gdk/macos/GdkMacosTile.c
+++ b/gdk/macos/GdkMacosTile.c
@@ -20,6 +20,8 @@
 
 #include "config.h"
 
+#include <AppKit/AppKit.h>
+
 #import "GdkMacosTile.h"
 
 @implementation GdkMacosTile