patch 8.2.3994: Vim9: extend() complains about type when it was not declared

Problem:    Vim9: extend() complains about the type even when it was not
            declared.
Solution:   Only check the list or dict type when it was declared.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3994,
 /**/
     3993,
 /**/