update docker image path to docker pull include org

[mmunro-ltrr]

Shouldn't the org name be inserted before the repository name when defining the prefix (line 36), rather than in front of everything including the registry name? I think the syntax is docker.pkg.github.com/org/repo/image:tag, but it may all be obsolete anyway https://github.blog/2020-09-01-introducing-github-container-registry/