Section D.3: "If you're posting anything you did not create yourself or do not own the rights to, you agree that you are responsible for any Content you post". A lawsuit against Github has no standing for the scenario you suggest, because Github is not at fault.
Well, I don't think it's a DCMA issue, but it does very much depend on the licence you have chosen. That's what the licence is for, to allow people to use the code that you have copyright of, and to define what they are / are not allowed to do with it.
