fix(vim.lsp): replace deprecated vim.lsp.start_client with vim.lsp.start

==============================================================================
vim.deprecated:
require("vim.deprecated.health").check()

 ~
- WARNING vim.lsp.start_client() is deprecated. Feature will be removed
in Nvim 0.13
  - ADVICE:
    - use vim.lsp.start() instead.
    - stack traceback:

/home/USER/.local/share/nvim/lazy/copilot.vim/lua/_copilot.lua:34

Author: alexpasmantier

lua/_copilot.lua

@@ -31,7 +31,7 @@ copilot.lsp_start_client = function(cmd, handler_names, opts, settings)
   -- start_client() is deprecated, but the replacement start() breaks our
   -- restart workflow by returning the old client that's shutting down.
   -- https://github.com/neovim/neovim/issues/33616
-  id = vim.lsp.start_client({
+  id = vim.lsp.start({
     cmd = cmd,
     cmd_cwd = vim.call('copilot#job#Cwd'),
     name = 'GitHub Copilot',