GITHUB_WORKSPACE not mounted in Actions Docker container

I’m trying to develop my first GitHub Action that uploads code coverage for Node.js projects to Code Climate.

I have a draft version at https://github.com/paambaati/codeclimate-action, and have it set up as an action on another project at https://github.com/paambaati/websight

Now when I run the action (see one such run at https://github.com/paambaati/websight/runs/189324965), the GITHUB_WORKSPACE doesn’t seem to be mounted like the documentation says. You can see that /github doesn’t exist, and env doesn’t seem to print any GITHUB_* variables either.

What am I doing wrong?

Closed as duplicate of https://github.community/t5/GitHub-API-Development-and/GITHUB-WORKSPACE-not-mounted-in-Actions-Docker-container/m-p/28874#M2490