patch 8.2.2193: Vim9: can change constant in :def function

Problem:    Vim9: can change constant in :def function.
Solution:   Check if a variable is locked. (issue #7526)
diff --git a/src/proto/evalvars.pro b/src/proto/evalvars.pro
index 4c9d645..c597ca3 100644
--- a/src/proto/evalvars.pro
+++ b/src/proto/evalvars.pro
@@ -70,6 +70,7 @@
 void delete_var(hashtab_T *ht, hashitem_T *hi);
 void set_var(char_u *name, typval_T *tv, int copy);
 void set_var_const(char_u *name, type_T *type, typval_T *tv_arg, int copy, int flags);
+int var_check_permission(dictitem_T *di, char_u *name);
 int var_check_ro(int flags, char_u *name, int use_gettext);
 int var_check_lock(int flags, char_u *name, int use_gettext);
 int var_check_fixed(int flags, char_u *name, int use_gettext);