IDE Web Terminal 404 in staging

(Identified in gitlab-org/release/tasks#595 (comment 124375646))

Description:

I am getting 404 from the terminal.ws websocket request. When I resend this request through the Network Tab, I get another 404 status but a 403 response.

Screenshot:

Investigation:

• I'm using the shared runners which are all docker. Could that be causing the issue?
• Is my user missing some privilege to actually run this, which isn't being checked in check_config?