Some mistakes turned up by FindBugs and BuildTriggerTest stack traces.
No sense in spending ~20s running HtmlUnit to verify code which has since been deleted anyway (configuration-time ACL checks).
Unnecessary and misleading for a QueueItemAuthenticator to be a @TestExtension.
(It may have a @TestExtension QueueItemAuthenticatorDescriptor if one is needed.)
Introduced MockQueueItemAuthenticator as a convenience.