Update docker image tag format in workflow file

Author: dkruyt

.github/workflows/docker-image.yml

@@ -34,4 +34,4 @@ jobs:
         context: .
         push: true
         tags: |
-          ghcr.io/${{ github.repository }}:${{ github.event.repository.name }}:${{ github.ref_name }}
+          ghcr.io/${{ github.repository }}/${{ github.event.repository.name }}:${{ github.ref_name }}