Git has all sorts of options for using proxies, but running socat would be the quick and dirty way to do this, something like:

  socat TCP-LISTEN:8080,fork,reuseaddr OPENSSL:github.com:443

would let you use an HTTP connection to your less archaic machine. Could even configure git to automatically do the rewrite similar to https://stackoverflow.com/questions/1722807/how-to-convert-g.... There's security considerations here so don't just do this blindly, but if no more unencrypted git protocol is a real pain point there's pain free ways around it.