nvim: after/plugin/statusline: Use nvim_set_hl API

See https://github.com/neovim/neovim/pull/17187.

nvim/.config/nvim/after/plugin/statusline.lua

@@ -20,7 +20,7 @@ local colors = {
 }
 
 local function highlight(group, fg, bg)
-  cmd(string.format("%s %s %s %s %s %s", "highlight ", group, "guifg=", fg, "guibg=", bg))
+  api.nvim_set_hl(0, group, { fg = fg, bg = bg })
 end
 
 highlight("Window"      , colors.red    , colors.bg)