vim-patch:9.1.0705: Sorting of fuzzy filename completion is not stable

Problem:  Sorting of fuzzy filename completion is not stable
Solution: Compare indexes when scores are equal.  Fix some typos.
          (zeertzjq)

closes: vim/vim#15593

58d705238c

test/functional/ui/popupmenu_spec.lua

@@ -6955,9 +6955,9 @@ describe('builtin popupmenu', function()
           {2:-- }{5:match 2 of 3}                 |
         ]])
 
-        feed('<Esc>S/non_exit_folder<C-X><C-F>')
+        feed('<Esc>S/non_existing_folder<C-X><C-F>')
         screen:expect([[
-          /non_exit_folder^                |
+          /non_existing_folder^            |
           {1:~                               }|*18
           {2:-- }{6:Pattern not found}            |
         ]])