Minor change to ArcanistInfrastructureTestCase
Summary: Update ArcanistInfrastructureTestCase after D9860 and D9861.
Test Plan: arc unit should do the trick.
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D9863