If I was in the group chat, yes. U of T states that if you know of academic dishonesty but don't act upon it then you are also considered guilty. Just leaving the group chat wouldn't be enough if anything comes of it as there is a digital record of your presence/departure. Sorry, but I wouldn't risk my own standing over something that someone else did. I've thankfully never been in this situation but I'm assuming that everyone who reports it is let off the hook so I think everyone who sees it should report it. In this case you should save yourself because it's your money and education and unfortunately not actively participating in cheating but remaining silent just isn't enough to get out of an academic dishonesty penalty.