True, but it doesn't mention doing so without the attribution that might be required by the code's licence. If full attribution of where the suggestion was derived from was included¹ there would be not issue IMO², it is this matter that creates the grey area which these discussions result from.
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[1] the practicality³ of this is a different, though related, discussion
[2] because the user is fully informed and can take responsibility for the decision to use the suggestion or not
[3] or impossibility – given the code could be added by someone who doesn't include that attribution/licence information for the system to be able to pass on even if it were designed to
The terms of service are completely independent of the code's license. The code could say "no one but I may use this", but by using GitHub you give them rights to do everything stated in the Terms of Service.
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.
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.
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[1] the practicality³ of this is a different, though related, discussion
[2] because the user is fully informed and can take responsibility for the decision to use the suggestion or not
[3] or impossibility – given the code could be added by someone who doesn't include that attribution/licence information for the system to be able to pass on even if it were designed to