We currently limit Bake build to a single target: https://github.com/docker/github-builder-experimental/blob/e875129c872af249a9411fc0b1b1d1fe79ee6ddf/.github/workflows/bake.yml#L226-L228

Mainly because we don't have a way to discern which generated tags are associated to a target but also because a target could output build result locally while another one would push to registry.

We should document this but also explain how users can use a matrix strategy to solve this issue. For example using our matrix subaction: https://github.com/docker/bake-action/tree/master/subaction/matrix