docker login does not work with Quay about earthly

[vladaionescu]

I'm able to reproduce it even with docker hub and I'm seeing some consistency in behavior, although strange:

earth prune --reset (eliminate any cache)
docker rmi -f <image> (this is so that the docker pull is no cached in any way)

earth --no-cache +build (using a FROM with a private reg)  <-- fails consistently

docker pull <image>
earth --no-cache +build (using a FROM with a private reg)  <-- succeeds consistently

Unknown why the docker pull has anything to do with it.