When Git is not available on the runner, getSource() downloads the
repository using the REST API and returns early, before the commit
output is set. The ref output is still set by main.ts after getSource()
returns, so the step reports a ref but an empty commit, even though
action.yml documents commit unconditionally.
Set the output from the resolved settings on that path. The REST API
fallback does not create a local Git repository, so git log -1 cannot be
used there.