Fix 'Branches' typo in ActionsManagementPanel

Summary:
Fix typo 'Branches' in the panel header for the Diffusion Actions
management panel.

Test Plan: Saw 'Actions' in the panel heading

Reviewers: chad, epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D16654