patch 9.0.1867: Vim9: access to interface statics possible

Problem:  Vim9: access to interface statics possible
Solution: Prevent direct access to interface statics

closes: #13007

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Ernie Rael <errael@raelity.com>
diff --git a/src/errors.h b/src/errors.h
index c0e98df..e719ffd 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3513,5 +3513,6 @@
 	INIT(= N_("E1407: Member \"%s\": type mismatch, expected %s but got %s"));
 EXTERN char e_aptypes_is_null_str_nr[]
 	INIT(= "E1408: Internal error: ap_types or ap_types[idx] is NULL: %s: %d");
-
+EXTERN char e_interface_static_direct_access_str[]
+	INIT(= N_("E1409: Cannot directly access interface \"%s\" static member \"%s\""));
 // E1371 - E1399 unused