If you spin up your own Docker containers then yes, you cannot expose ports to the (Docker) host. I believe the reason for this is that the permissions required to do so would also give you permissions to the networking stack that would affect other customers, and that would not be acceptable for security reasons.
However, the two Minio images you have in your config can expose ports, and they will be connected to the same port on the build server localhost, using some CircleCI networking magic.
Finally, you can solve the first restriction by using Docker Compose - while you cannot publish ports in Docker, you can use internal Docker networking. So, if you want to connect to a Docker service, do it from another container on the same virtual network.