patch 8.2.0987: Vim9: cannot assign to [var; var]

Problem:    Vim9: cannot assign to [var; var].
Solution:   Assign rest of items to a list.
diff --git a/src/proto/list.pro b/src/proto/list.pro
index bdbf7eb..07dd4e2 100644
--- a/src/proto/list.pro
+++ b/src/proto/list.pro
@@ -33,6 +33,7 @@
 void f_flatten(typval_T *argvars, typval_T *rettv);
 int list_extend(list_T *l1, list_T *l2, listitem_T *bef);
 int list_concat(list_T *l1, list_T *l2, typval_T *tv);
+list_T *list_slice(list_T *ol, long n1, long n2);
 list_T *list_copy(list_T *orig, int deep, int copyID);
 void vimlist_remove(list_T *l, listitem_T *item, listitem_T *item2);
 char_u *list2string(typval_T *tv, int copyID, int restore_copyID);