Update container.yml

Author: callumforrester

.github/workflows/container.yml

@@ -1,3 +1,5 @@
+
+  
 name: Container CI
 
 on:
@@ -46,14 +48,18 @@ jobs:
       - name: Set up Docker Buildx
         id: buildx
         uses: docker/setup-buildx-action@v1
+      
+      - id: read-docker-image-identifiers
+        name: Read Docker Image Identifiers
+        run: echo "IMAGE_REPOSITORY=$(echo ${{ github.repository }} | tr '[:upper:]' '[:lower:]')" >> $GITHUB_ENV
 
       - name: Run build (base container)
         uses: docker/build-push-action@v2
         with:
           builder: ${{ steps.buildx.output.name }}
           push: true
           tags: |
-            ghcr.io/$(echo ${{ github.repository }} | tr '[:upper:]' '[:lower:]'):${{ steps.tagger.outputs.image_tag }}
+            ghcr.io/${{ env.IMAGE_REPOSITORY }}:${{ steps.tagger.outputs.image_tag }}
           target: base
           cache-from: type=local,src=~/cache
           cache-to: type=local,dest=~/cache