patch 9.0.1290: CTRL-N and -P on cmdline don't trigger CmdlineChanged

Problem:    CTRL-N and -P on cmdline don't trigger CmdlineChanged.
Solution:   Jump to cmdline_changed instead of cmdline_not_changed.
            (closes #11956)
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index 8931678..c11f6ff 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -1918,6 +1918,41 @@
   au! CmdlineChanged
   cunmap <F1>
 
+  let g:log = []
+  autocmd CmdlineChanged : let g:log += [getcmdline()]
+  call feedkeys(":sign \<Tab>\<Tab>\<C-N>\<C-P>\<S-Tab>\<S-Tab>\<Esc>", 'xt')
+  call assert_equal([
+        \ 's',
+        \ 'si',
+        \ 'sig',
+        \ 'sign',
+        \ 'sign ',
+        \ 'sign define',
+        \ 'sign jump',
+        \ 'sign list',
+        \ 'sign jump',
+        \ 'sign define',
+        \ 'sign ',
+        \ ], g:log)
+  let g:log = []
+  set wildmenu wildoptions+=pum
+  call feedkeys(":sign \<S-Tab>\<PageUp>\<kPageUp>\<kPageDown>\<PageDown>\<Esc>", 'xt')
+  call assert_equal([
+        \ 's',
+        \ 'si',
+        \ 'sig',
+        \ 'sign',
+        \ 'sign ',
+        \ 'sign unplace',
+        \ 'sign jump',
+        \ 'sign define',
+        \ 'sign undefine',
+        \ 'sign unplace',
+        \ ], g:log)
+  set wildmenu& wildoptions&
+  unlet g:log
+  au! CmdlineChanged
+
   au! CmdlineEnter : let g:entered = expand('<afile>')
   au! CmdlineLeave : let g:left = expand('<afile>')
   let g:entered = 0