vim-patch:9.1.1121: Enter does not insert newline with "noselect"

Problem:  Enter does not insert newline with "noselect" when the pum is
          visible (lifepillar)
Solution: When Enter is pressed and no complete-item is selected,
          ins_compl_prep returns false, and the edit function continues
          processing Enter to insert a new line. (glepnir)

fixes: vim/vim#1653
closes: vim/vim#16653

07f0dbe3aa

Co-authored-by: glepnir <glephunter@gmail.com>

test/functional/editor/completion_spec.lua

@@ -506,19 +506,21 @@ describe('completion', function()
       ]])
     end)
 
-    it('Enter selects original text after adding leader', function()
+    it('Enter selects original text after adding leader and insert newline', function()
       feed('iJ<C-x><C-u>')
       poke_eventloop()
       feed('u')
       poke_eventloop()
       feed('<CR>')
-      expect('Ju')
+      expect([[Ju
+]])
       feed('<Esc>')
       poke_eventloop()
       -- The behavior should be the same when completion has been interrupted,
       -- which can happen interactively if the completion function is slow.
-      feed('SJ<C-x><C-u>u<CR>')
-      expect('Ju')
+      feed('ggVGSJ<C-x><C-u>u<CR>')
+      expect([[Ju
+]])
     end)
   end)