Use setlocal for temporary completeopt adjustment

Since vim 9.1.0469, completeopt is a global-local option.  When adding
`noselect`, we need to treat `completeopt` as local and use `setlocal`.
This works for 9.1.0016 as well and allows users to freely mess with
buffer-local `completeopt` without messing up YCM completions.

autoload/youcompleteme.vim

@@ -1357,7 +1357,7 @@ function! s:Complete()
   endif
   if len( s:completion.completions )
     let old_completeopt = &completeopt
-    set completeopt+=noselect
+    setlocal completeopt+=noselect
     call complete( s:completion.completion_start_column,
                  \ s:completion.completions )
     let &completeopt = old_completeopt