wrong command to emacs-ssg.el does not output an error

In this case https://gitlab.com/sctlib/piano/-/jobs/5827004737#L732 pusblish vs publish the program should output an error.

It says:

emacs-ssg.el unkown command
Error: (file-missing "Searching for program" "No such file or directory" "git")

But then then gitlab pages continues the upload of artifacts (when none were really produced).