Add TestGitoHTTPWebhookDeliveryEnqueuesCreationSyncOnce to prove that a
signed HTTP branch.updated delivery reaches gitoBridgeHTTPAdapter, triggers
the bridge scanner, and enqueues exactly one RoadmapCreationSync job.
Also adds TestGitoHTTPWebhookDeliveryRejectedOnInvalidSignature and
TestGitoHTTPWebhookDeliveryOffTargetIgnored for completeness.
