patch 9.0.1453: typos in source code and tests

Problem:    Typos in source code and tests.
Solution:   Fi the typos. (Dominique Pellé, closes #12217)
diff --git a/src/testdir/test_menu.vim b/src/testdir/test_menu.vim
index 1247359..9929dd5 100644
--- a/src/testdir/test_menu.vim
+++ b/src/testdir/test_menu.vim
@@ -162,7 +162,7 @@
 
 " Test for menu item completion in command line
 func Test_menu_expand()
-  " Create the menu itmes for test
+  " Create the menu items for test
   menu Dummy.Nothing lll
   for i in range(1, 4)
     let m = 'menu Xmenu.A' .. i .. '.A' .. i