fix: treesitter markdown italic

[xudyang1]

No description provided.

[xudyang1]

Current workaround with overrides:

require("gruvbox").setup({
  overrides = {
    ["@markup.italic"] = {
      italic = true,
    },
  }
}

With this pull request, italic works correctly without overrides.

[ellisonleao]

thanks @xudyang1 , can you make it a link to @text.emphasis instead please?

[xudyang1]

thanks @xudyang1 , can you make it a link to @text.emphasis instead please?

Yes, the code is updated