You can't edit a wiki page in WYSIWYG mode if you can't connect to the realtime session

Steps to reproduce:

• Edit the XWiki.Realtime.Configuration page in object mode, expand the first UIExtensionClass object, look for the webSocketURL configuration and replace "netflux" with something else, e.g. "bad-netflux". The purpose of this is to simulate a bad WebSocket upgrade request. Note that blocking the "netflux" request using the browser's Network tab doesn't have the same effect. We want to simulate the fact that an HTTP proxy in front of XWiki doesn't forward the WebSocket requests properly.
• Edit a plain wiki page using the default in-place WYSIWYG edit mode

Expected: the user should be notified that we failed to connect to the realtime session, and they should be able to continue editing alone (outside realtime session).

Actual: the edit mode toolbar is hidden, and the user can't edit the content (they see a spinning wheel when hovering the content)