Fixup GHCR manifest job

Author: Apsu

.github/workflows/build-vllm.yaml

@@ -69,6 +69,10 @@ jobs:
     needs: build
     runs-on: self-hosted
     steps:
+      - name: Generate image name
+        run: |
+          echo "GHCR_IMAGE=ghcr.io/${GITHUB_REPOSITORY@L}" >> ${GITHUB_ENV}
+
       - name: Login to GHCR
         uses: docker/login-action@v3
         with: