Fix incorrect error class for raise_on_open_redirects in guide

The error was changed from `ArgumentError` to `UnsafeRedirectError` in:
rails@c3758a7

Author: walro

guides/source/configuring.md

@@ -1355,7 +1355,7 @@ Rendered recordings/threads/_thread.html.erb in 1.5 ms [cache miss]
 
 #### `config.action_controller.raise_on_open_redirects`
 
-Raises an `ArgumentError` when an unpermitted open redirect occurs.
+Raises an `ActionController::Redirecting::UnsafeRedirectError` when an unpermitted open redirect occurs.
 
 The default value depends on the `config.load_defaults` target version: