refactor api call that will be deprecated

[ChausseBenjamin]

Fixes this checkhealth issue:

- ⚠️ WARNING vim.lsp.get_buffers_by_client_id() is deprecated. Feature will be removed in Nvim 0.13
  - ADVICE:
    - use vim.lsp.get_client_by_id(id).attached_buffers instead.
    - stack traceback:
        ~/.local/share/nvim/site/pack/core/opt/rustaceanvim/lua/rustaceanvim/server_status.lua:52
        ~/.local/share/bob/nightly/share/nvim/runtime/lua/vim/lsp/client.lua:1194
        ~/.local/share/bob/nightly/share/nvim/runtime/lua/vim/lsp/client.lua:449
        vim/_editor.lua:0

Note that I'm currently on the nightly build of Neovim

[github-actions]

Review Checklist

Does this PR follow the Contribution Guidelines? Following is a partial checklist:

Proper conventional commit scoping:

• For example, fix(lsp): some lsp-related bugfix

• Pull request title has the appropriate conventional commit prefix.

If applicable:

• Tested
  • Tests have been added.
  • Tested manually (Steps to reproduce in PR description).
• Updated documentation.

[mrcjkb]

Thanks for the PR 🙏

• Have you also tested this change in Neovim 0.11?

CI is failing on the lua-ls type checks:

Warning: lua/rustaceanvim/server_status.lua:53:42 [Warning] Cannot assign `true` to `integer?`.
       > - `true` cannot match `integer?`
       > - Type `true` cannot match `nil`
       > - Type `true` cannot match `integer` (assign-type-mismatch)
       >           if vim.lsp.inlay_hint.is_enabled { bufnr = bufnr } then
       >                                              ^^^^^

See https://github.com/mrcjkb/rustaceanvim/blob/master/CONTRIBUTING.md#type-safety

Note

I have a weekly cron job that updates the
Neovim nightly pin and runs CI and fails if there's a new deprecation
(as long as it's annotated with ---@deprecated).
That's when I typically fix nightly deprecation warnings.

[mrcjkb]

fe91aad