nixos/tests/xmpp: fix after xmpp >= 1.9
`ClientXMPP.process` is gone but trivial to diy in our case.see https://slixmpp.readthedocs.io/en/latest/howto/remove_process.html
Willy 7 months ago b80cb24a 8e166f7a
··· 98 98 # MUC 99 99 ct.register_plugin('xep_0045') 100 100 ct.connect(("${connectTo}", 5222)) 101 101 - ct.process(forever=False) 101 101 + ct.loop.run_until_complete(ct.disconnected) 102 102 103 103 if not ct.test_succeeded: 104 104 sys.exit(1)