I think it's unlikely. Github were on cloud, and then moved to their own infrastructure a while back. In fact they have their own provisioning framework and all that fun stuff.
I doubt they will move back to Azure or any cloud for that matter. It's the same story with Dropbox and similar companies. Once past a point in scale, and depending on the case, for example need to control the data security to have certain certifications, it's essential to have your own infrastructure.
Microsoft owns Azure, Microsoft owns GitHub. Azure is Microsoft’s own infrastructure. Remember kids there is no cloud it’s just somebody else’s computer.
I doubt they will move back to Azure or any cloud for that matter. It's the same story with Dropbox and similar companies. Once past a point in scale, and depending on the case, for example need to control the data security to have certain certifications, it's essential to have your own infrastructure.