patch 8.2.1813: Vim9: can assign wrong type to script dict

Problem:    Vim9: can assign wrong type to script dict. (Christian J.  Robinson)
Solution:   Check the type if known.
diff --git a/src/proto/evalvars.pro b/src/proto/evalvars.pro
index 6965508..520fedd 100644
--- a/src/proto/evalvars.pro
+++ b/src/proto/evalvars.pro
@@ -58,6 +58,7 @@
 void check_vars(char_u *name, int len);
 dictitem_T *find_var(char_u *name, hashtab_T **htp, int no_autoload);
 dictitem_T *find_var_in_ht(hashtab_T *ht, int htname, char_u *varname, int no_autoload);
+hashtab_T *get_script_local_ht(void);
 void *lookup_scriptvar(char_u *name, size_t len, cctx_T *dummy);
 hashtab_T *find_var_ht(char_u *name, char_u **varname);
 char_u *get_var_value(char_u *name);