Comment by geerlingguy

A PR was posted within a minute or two of PHP's source code update. Then within a minute of the PR's CI job completing, it was merged, and the build took a while but is now complete: https://github.com/docker-library/php/actions/runs/396158697...

It would not be easy (or reasonable) to take a public build like that private to build a 'secret' image version, and I'm not sure GitHub even has the capability to do that. I would not trust a build pushed to Docker Hub separate from the established / public / auditable process they have in place.