patch 8.2.4225: Vim9: depth argument of :lockvar not parsed in :def function

Problem:    Vim9: depth argument of :lockvar not parsed in :def function.
Solution:   Parse the optional depth argument. (closes #9629)
            Fix that locking doesn't work for a non-materialize list.
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 1232b35..a45d7c5 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -1754,7 +1754,8 @@
 	{
 	    listitem_T *li = list_find(list, lidx);
 
-	    if (error_if_locked(li->li_tv.v_lock, e_cannot_change_list_item))
+	    if (error_if_locked(li->li_tv.v_lock,
+					     e_cannot_change_locked_list_item))
 		return FAIL;
 	    // overwrite existing list item
 	    clear_tv(&li->li_tv);
@@ -1762,7 +1763,7 @@
 	}
 	else
 	{
-	    if (error_if_locked(list->lv_lock, e_cannot_change_list))
+	    if (error_if_locked(list->lv_lock, e_cannot_change_locked_list))
 		return FAIL;
 	    // append to list, only fails when out of memory
 	    if (list_append_tv(list, tv) == FAIL)