[gtk] Add includes back to gtk4.types.in

[Matthias Clasen <matthiasc src gnome org>]

commit 1be850d80619bab5b4b03480305735e15f74999b
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Jun 22 20:24:26 2019 -0400

    Add includes back to gtk4.types.in
    
    Without these, gtkdoc-scangobj doesn't work. Who knew!

 docs/reference/gtk/gtk4.types.in | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/docs/reference/gtk/gtk4.types.in b/docs/reference/gtk/gtk4.types.in
index 0cfaf1c4e4..8073f3ad20 100644
--- a/docs/reference/gtk/gtk4.types.in
+++ b/docs/reference/gtk/gtk4.types.in
@@ -1,3 +1,6 @@
+#include <gtk/gtk.h>
+#include <gtk/gtkunixprint.h>
+
 gtk_about_dialog_get_type
 gtk_accel_group_get_type
 gtk_accel_label_get_type