GHSA-5957-C7QM-M469 Action Mailbox: Possible signature replay in Action Mailbox Mailgun ingress

Impact The Action Mailbox Mailgun ingress authenticates a request with an HMAC of the timestamp and token parameters concatenated without a separator, and ActionMailbox::Ingresses::Mailgun::InboundEmailsController::Authenticatorrecent? rejects only timestamps more than 2 minutes in the past...