trivy-action@v0.29.0 internally uses setup-trivy@v0.2.2, a tag removed
upstream (earliest published is now v0.2.6), so it cannot resolve on any
runner. Run trivy from a digest-pinned image instead, as gitleaks already is.
RUNBOOK gains a 'Setting up CI/CD from scratch' section with the traps that
actually cost time: GITEA_TOKEN is 401 at the package registry, the runner's
cache fails soft, service containers resolve by name not localhost.
Not pushed: pushing triggers a run, and the runner is being restarted by the
ansible change that enables its cache.