FIX: Don’t raise an error on permalinks with external URL

Currently redirecting to an external URL through a permalink doesn’t
work because Rails raises a
`ActionController::Redirecting::UnsafeRedirectError` error.

This wasn’t the case before we upgraded to Rails 7.0.

This patch fixes the issue by using `allow_other_host: true` on the
redirect.

app/controllers/permalinks_controller.rb

@@ -11,7 +11,7 @@ class PermalinksController < ApplicationController
     raise Discourse::NotFound unless permalink
 
     if permalink.target_url
-      redirect_to permalink.target_url, status: :moved_permanently
+      redirect_to permalink.target_url, status: :moved_permanently, allow_other_host: true
     else
       raise Discourse::NotFound
     end