docs: correct type for render option

lua/notify/init.lua

@@ -47,7 +47,7 @@ end
 ---@field on_open function: Callback for when window opens, receives window as argument.
 ---@field on_close function: Callback for when window closes, receives window as argument.
 ---@field keep function: Function to keep the notification window open after timeout, should return boolean.
----@field render function: Function to render a notification buffer.
+---@field render function|string: Function to render a notification buffer.
 ---@field replace integer | notify.Record: Notification record or the record `id` field. Replace an existing notification if still open. All arguments not given are inherited from the replaced notification including message and level.
 ---@field hide_from_history boolean: Hide this notification from the history
 ---@field animate boolean: If false, the window will jump to the timed stage. Intended for use in blocking events (e.g. vim.fn.input)