Fix failing test in PhabricatorPolicyDataTestCase caused by membership locking
Summary: This fixes a unit test failure that started occurring due to the new membership locking feature.
Test Plan: Ran the unit tests.
Reviewers: btrahan, epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D10546