mod_pubsub_summary: Use pre-escaped UTF-8 sequence for compat This silences a warning about using the non-existent global 'utf8' each time this line was hit. The utf8 library was introduced in Lua 5.3, so the warning would appear with 5.1 and 5.2.

module:hook("authentication-success", function (event)
	local session = event.session;
	local sasl_handler = session.sasl_handler;
	session.log("info", "Authenticated with %s", sasl_handler and sasl_handler.selected or "legacy auth");
end);