Lets not forget that certificates are created and checked for github.com, so unlikely for a middleman to get in.
I trust github much more than google right now. Especially since the object being fetched is generic as opposed to a appstore. Google's app store has only shown to hinder publishing. Take syncthing for instance.
The only thing I wish was better was the .apk selection process. It would be nice if a database existed with filename formats or a little extra metadata to match the correct asset.