Make the external_audit_event_destination URL unique

Signed-off-by: Rémy Coutable <remy@rymai.me>

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
-    destination_url { FFaker::Internet.http_url }
+    sequence(:destination_url) { |n| "#{FFaker::Internet.http_url}/#{n}" }
   end
 end