patch 8.2.2680: Vim9: problem defining a script variable from legacy function

Problem:    Vim9: problem defining a script variable from legacy function.
Solution:   Check if the script is Vim9, not the current syntax.
            (closes #8032)
diff --git a/src/evalvars.c b/src/evalvars.c
index e9e893a..a482453 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -3168,6 +3168,7 @@
     hashtab_T	*ht;
     int		is_script_local;
     int		vim9script = in_vim9script();
+    int		var_in_vim9script;
 
     ht = find_var_ht(name, &varname);
     if (ht == NULL || *varname == NUL)
@@ -3186,6 +3187,7 @@
 	vim9_declare_error(name);
 	goto failed;
     }
+    var_in_vim9script = is_script_local && current_script_is_vim9();
 
     di = find_var_in_ht(ht, 0, varname, TRUE);
 
@@ -3217,7 +3219,7 @@
 		goto failed;
 	    }
 
-	    if (is_script_local && vim9script)
+	    if (var_in_vim9script)
 	    {
 		where_T where;
 
@@ -3244,7 +3246,7 @@
 
 	    // A Vim9 script-local variable is also present in sn_all_vars and
 	    // sn_var_vals.  It may set "type" from "tv".
-	    if (is_script_local && vim9script)
+	    if (var_in_vim9script)
 		update_vim9_script_var(FALSE, di, flags, tv, &type);
 	}
 
@@ -3308,7 +3310,7 @@
 	}
 
 	// add a new variable
-	if (vim9script && is_script_local && (flags & ASSIGN_NO_DECL))
+	if (var_in_vim9script && (flags & ASSIGN_NO_DECL))
 	{
 	    semsg(_(e_unknown_variable_str), name);
 	    goto failed;
@@ -3342,7 +3344,7 @@
 
 	// A Vim9 script-local variable is also added to sn_all_vars and
 	// sn_var_vals. It may set "type" from "tv".
-	if (is_script_local && vim9script)
+	if (var_in_vim9script)
 	    update_vim9_script_var(TRUE, di, flags, tv, &type);
     }