Merge pull request #5 from lf-edge/ci-tags

no need for derived tags when building ephemeral images in CI

Author: deitch

.github/workflows/prbuild.yaml

@@ -41,6 +41,5 @@
             platforms: linux/amd64,linux/arm64
             push: false
             tags: |
-              ${{ github.event.pull_request.head.repo.full_name }}:${{ github.event.pull_request.head.ref }}
               ${{ github.event.pull_request.head.repo.full_name }}:latest