Quick actions no longer work with Monaco settings editor

Created by: LawnGnome

I've bisected this down to 948ca3523d1f7188ca1aa395b087632b55d6ce92, added by #36033, but haven't yet figured out what the right fix would be. Will have a quick bash at this; otherwise will pass it off to someone with more knowledge.

It looks like this change means that the subscriptions are never added, which means that this.configEditor is never set, which causes this check to fail and the alert() to fire.

To reproduce what I saw:

1. Go to Site Admin -> Manage Code Hosts.
2. Edit any host.
3. Click on a quick action button (eg Add Webhook for a GitHub code host).
4. Observe the alert().