use correct git tag source

.github/workflows/build-publish.yml

@@ -28,17 +28,12 @@ jobs:
       with:
         string: ${{ github.repository }}
 
-    - name: set current date as env variable
-      id: version
-      run: |
-        echo "builddatetime=$(date +'%Y%m%dT%H%M%S')" >> $GITHUB_OUTPUT
-
     - name: build and push Docker image
       uses: docker/build-push-action@v5
       with:
         push: true
         tags: |
-          ghcr.io/${{ steps.lower-repo.outputs.lowercase }}:latest,ghcr.io/${{ steps.lower-repo.outputs.lowercase }}:${{ steps.vars.outputs.tag }}
+          ghcr.io/${{ steps.lower-repo.outputs.lowercase }}:latest,ghcr.io/${{ steps.lower-repo.outputs.lowercase }}:${{ github.ref_name }}
         platforms: linux/amd64,linux/arm64
         # https://docs.docker.com/build/ci/github-actions/cache/#cache-backend-api
         cache-from: type=gha