ci: gate feature publishing on successful tests

[mikaello]

Change

Make failed feature tests fail CI, while allowing the full matrix to finish.
Run feature publication only after a successful CI workflow for a push to main and check out the tested commit.
This prevents a broken feature from being published while its tests are still running or failing.

The feature-starter template supplies the repository structure and release action, but its current workflow has continue-on-error: true and uses manual publication.
This PR keeps the existing publish action and improves the release gate for this repository.

Validation

• Both workflows parse as YAML.
• git diff --check passes.
• PR CI runs the existing feature test matrix.

References

• https://github.com/devcontainers/feature-starter/tree/main/.github/workflows
• https://docs.github.com/en/actions/reference/workflows-and-actions/events-that-trigger-workflows#workflow_run