The docker://zricethezav/gitleaks action mounts the workspace at
/github/workspace, but --source pointed at the host path from
github.workspace ($HOME/runner/work/...), which does not exist inside the
container -> 'stat ...: no such file or directory' on every run.
Follow the 2dph canon (ci.yml secret-scan): install the gitleaks binary
instead of the docker action and scan GITHUB_WORKSPACE - works on both
GitHub and Gitea act runners.