Use static known URL for ExternalAuditEventDestination factory

Previously, a random generated URL could point to a valid IP which might
be considered as "local network" or "loopback" by Gitlab::UrlBlocker and
fail during record creation with:

Validation failed: Destination url is blocked: Requests to loopback
addresses are not allowed

example.org is a known, static and public URL.

ee/spec/factories/audit_events/external_audit_event_destinations.rb

@@ -3,6 +3,6 @@
 FactoryBot.define do
   factory :external_audit_event_destination, class: 'AuditEvents::ExternalAuditEventDestination' do
     group
-    sequence(:destination_url) { |n| "#{FFaker::Internet.http_url}/#{n}" }
+    sequence(:destination_url) { |n| "http://example.org/#{n}" }
   end
 end