add core tag, still maintain deprecated proxy tag

.github/workflows/container.yml

@@ -25,13 +25,11 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
-      - name: Lowercase and set image tag
-        run: echo "IMAGE_TAG=ghcr.io/proxy:latest" >> $GITHUB_ENV
-
       - name: Build and push Docker image
         uses: docker/build-push-action@v4
         with:
           context: .
           push: true
           tags: |
-            ${{ env.IMAGE_TAG }}
+            ghcr.io/routstr/proxy:latest
+            ghcr.io/routstr/core:latest