disable the foreach macro for gtk4

gintro/gimplgobj.nim

@@ -411,6 +411,9 @@ gtk_container_foreach (
   gpointer callback_data
 )
 ]#
+
+when not declared(gtk4): # only for old gtk3, gtk4 has no gtk.Container widget.
+
   # https://docs.gtk.org/gtk3/method.Container.foreach.html
   macro foreach*(container: gtk.Container; p: untyped; arg: typed): untyped =
     var foreachID {.compileTime, global.}: int
@@ -450,4 +453,4 @@ $1($5, $4)
     #echo r2s
     result = parseStmt(r1s & r2s)
 
-# 453 lines
+# 456 lines