The "Chatting with some friend over XMPP in a multi-user chat" scenario is broken on Riseup MUCs

When connecting to a MUC, a dialog opens recommending OMEMO, OTR or PGP for MUCs. So this test scenario cannot pass. I assume that detecting and escaping this dialog should be trivial, hence the (close) target version, but feel free to postpone.

Parent Task: #10288

Original created by @intrigeri on 12558 (Redmine)