Filtering by milestone in the global issues list is broken

To reproduce:

1. Go to your global issues list (e.g. https://gitlab.com/dashboard/issues?assignee_id=209240)
2. Click the "Milestone" dropdown and select a milestone
3. Page is not reloaded with the correct list of issues

cc @jschatz1

mentioned in issue #14939 (closed)

Reassigned to @iamphill

mentioned in commit 2f4dc45d

mentioned in merge request !3650 (merged)

Status changed to closed by merge request !3650 (merged)

mentioned in commit 4087bd16