Allow public on list of subscribers

Summary: Fixes T7317, allows public to be set on this list controller.

Test Plan: Tested a list of subscribers on a logged in and logged out Diff.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7317

Differential Revision: https://secure.phabricator.com/D11801

src/applications/subscriptions/controller/PhabricatorSubscriptionsListController.php

@@ -9,6 +9,10 @@ final class PhabricatorSubscriptionsListController
     $this->phid = idx($data, 'phid');
   }
 
+  public function shouldAllowPublic() {
+    return true;
+  }
+
   public function processRequest() {
     $request = $this->getRequest();