replace update_file method in gbRequest code

[rohith4444]

Right now, our gbContribute logic relies on the pygithub python module. In this module we rely on the update_file method, which does not support LFS. As all of our files are now stored on LFS, this is a challenge!

Eventually we should update this with subprocess calls, but for now we'll correct this by remapping to LFS during the builds. Leaving this issue here as a placeholder for the future.