Set lowercased image name in Docker publish workflow

Add step to set lowercased image name in environment

Author: TobEnd

.github/workflows/docker-publish.yml

@@ -25,7 +25,11 @@ jobs:
           registry: ${{ env.REGISTRY }}
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
-
+          
+      - name: Set lowercased image name
+        run: |
+          echo "IMAGE_NAME=${GITHUB_REPOSITORY,,}" >> $GITHUB_ENV
+          
       - name: Extract metadata
         id: meta
         uses: docker/metadata-action@v5