This is a derative of the workflow from tcardonne/docker-github-runner which does not expose the GITHUB_ACCESS_TOKEN as an env var to the runner environment! Instead, you must docker exec into the container after bringing it up and manually run:
docker exec -ti <container> bash
/entrypoint.sh <GITHUB_ACCESS_TOKEN>
to bring up the runner.
This builds the runner from the Ubuntu-based rocker/geospatial image, containing many commonly-used dependencies for R-based work.