fix(cmdwin): set 'buflisted'

Problem:
Legacy cmdwin set 'buflisted', but new one doesn't.
https://github.com/neovim/neovim/issues/40431#issuecomment-4811593353

'buflisted' useful for:
- "bufferline" style tablines, they usually show only listed buffers.
- some automatic actions can be conditioned on whether a buffer is
  listed; 'buflisted' signals that the buffer is "important enough".

Solution:
Set 'buflisted'.

runtime/lua/vim/_core/cmdwin.lua

@@ -74,7 +74,7 @@ function M.open(type, init_line, init_col)
   vim.bo[buf].buftype = 'nofile'
   vim.bo[buf].bufhidden = 'wipe'
   vim.bo[buf].swapfile = false
-  vim.bo[buf].buflisted = false
+  vim.bo[buf].buflisted = true -- #40431
   vim.wo[win][0].winfixbuf = true
   vim.wo[win][0].foldenable = false
   -- Show cmdwin-char via 'statuscolumn'.