patch 8.2.1996: Vim9: invalid error for argument of extend()

Problem:    Vim9: invalid error for argument of extend().
Solution:   Check if the type could match. (closes #7299)

src/vim9compile.c

@@ -820,7 +820,7 @@ generate_TYPECHECK(
  * Return TRUE if "actual" could be "expected" and a runtime typecheck is to be
  * used.  Return FALSE if the types will never match.
  */
-    static int
+    int
 use_typecheck(type_T *actual, type_T *expected)
 {
     if (actual->tt_type == VAR_ANY