When you upload code to Github, you agree to license it to them under Github's terms, and not whatever license the software is typically distributed under. You

When you upload code to Github, you agree to license it to them under Github's terms, and not whatever license the software is typically distributed under. You are effectively "dual licensing" software by uploading it to Github, whether you realize it or not. Of course, there are edge cases in which you don't have the rights to license the software to Github, but in those cases, I don't have the answer.