Doesn't work with Custom Docker locations

[sr-tennisgazelle]

This assumes the docker daemon on a server to always be running on unix:///var/run/docker.sock

While this might be fair, this doesn't account for the use case of a custom github runner, where the env var DOCKER_HOST is set.
In cases where it is set (say, i'm running this on ubuntu-latest rather than on custom-server-1), then it will get past the docker build and creation of the container, but it will fail when it gets to the docker run ... cmd as it will have taken DOCKER_HOST as a parameter there.

Basically, it's doomed if you provide the ENV VAR and it's doomed if you do not.