patch 9.0.0327: items() does not work on a list

Problem:    items() does not work on a list. (Sergey Vlasov)
Solution:   Make items() work on a list. (closes #11013)
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index bba4e3e..c87d701 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -198,6 +198,17 @@
   call v9.CheckDefAndScriptFailure(lines, 'E1012:', 2)
 endfunc
 
+func Test_list_items()
+  let r = []
+  let l = ['a', 'b', 'c']
+  for [idx, val] in items(l)
+    call extend(r, [[idx, val]])
+  endfor
+  call assert_equal([[0, 'a'], [1, 'b'], [2, 'c']], r)
+
+  call assert_fails('call items(3)', 'E1227:')
+endfunc
+
 " Test removing items in list
 func Test_list_func_remove()
   let lines =<< trim END