Summary: Fixes T9689, Always override `auth.email-domains` when running unit tests Test Plan: - Set `auth.email-domains` - Run `arc unit --everything`. Observe no errors. Reviewers: #blessed_reviewers, epriestley Reviewed By: #blessed_reviewers, epriestley Subscribers: Korvin Maniphest Tasks: T9689 Differential Revision: https://secure.phabricator.com/D14456