Update publish_image.yml

Author: vmbecerra

.github/workflows/publish_image.yml

@@ -30,4 +30,4 @@ jobs:
         uses: docker/build-push-action@v5
         with:
           push: true
-          tags: ghcr.io/${{ github.repository_owner }}/psopt-ci:latest
+          tags: ghcr.io/${{ github.repository_owner.toLower() }}/psopt-ci:latest