[dspillett]

But if the terms of service says nothing that is in contravention of your licence choice when you agree to them, then the service does something that you consider to be in contravention of your licence choice, what you have is one party unilaterally changing the agreement. Of course the exact legal meaning of the terms and any perceived change in them could and will be debated long, hard, and potentially expensively…

I'll stick to self-hosting instead of using services like GH. Keeps things a little more simple in that regard.

[Arainach]

The license agreement is irrelevant. Literally it does not come into play here. Github is not bound by the license; they are bound by the terms of service. The code is co-licensed: once however you declare it, once to Github independently.