T7646: Fix buildplan ac on Herald.

Summary: Fixes T7646.

Test Plan: Repeat steps described in T7646 and expect disabled build plans not displayed.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T7646

Differential Revision: https://secure.phabricator.com/D12133