neovim: a deprecated warning of `vim.lsp.buf_get_clients()` is shown

[AsPulse]

- ⚠️ WARNING vim.lsp.buf_get_clients() is deprecated. Feature will be removed in Nvim 0.12
  - ADVICE:
    - use vim.lsp.get_clients() instead.
    - stack traceback:
        /Users/aspulse/.local/share/nvim/lazy/symbols-outline.nvim/lua/symbols-outline/providers/nvim-lsp.lua:41
        /Users/aspulse/.local/share/nvim/lazy/symbols-outline.nvim/lua/symbols-outline/providers/init.lua:15
        /Users/aspulse/.local/share/nvim/lazy/symbols-outline.nvim/lua/symbols-outline.lua:161
        /Users/aspulse/.local/share/nvim/lazy/symbols-outline.nvim/lua/symbols-outline.lua:19