backport: fix(net): set buftype=nofile (again) (#39932)

redux 24e00f2844

(cherry picked from commit 1be55d02f5)

Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

runtime/plugin/net.lua

@@ -85,6 +85,7 @@ vim.api.nvim_create_autocmd('BufReadCmd', {
 
         vim.api.nvim_exec_autocmds('BufRead', { group = 'filetypedetect', buffer = ev.buf })
         vim.bo[ev.buf].modified = false
+        vim.bo[ev.buf].buftype = 'nofile'
         vim.notify(('Loaded %s'):format(url), vim.log.levels.INFO)
       end)
     )