ci: fix RELEASE_TAG env inject

.github/workflows/release.yaml

@@ -35,16 +35,21 @@ jobs:
         registry: ghcr.io
         username: ${{ github.repository_owner }}
         password: ${{ secrets.GITHUB_TOKEN }}
-        
+
+    - name: Set outputs
+      run: |
+        echo "RELEASE_TAG=${GITHUB_REF#refs/*/}" >> $GITHUB_ENV
+
     - name: Build and push image
       uses: docker/build-push-action@v2
       with:
         context: ./
         file: ./Dockerfile
         platforms: linux/amd64
-        push: true      
+        push: true
         cache-from: type=local,src=/tmp/.buildx-cache
         cache-to: type=local,dest=/tmp/.buildx-cache
         tags: |
           ghcr.io/grassrootseconomics/farmstar-survey-backend/farmstar-survey-backend:latest
           ghcr.io/grassrootseconomics/farmstar-survey-backend/farmstar-survey-backend:${{ env.RELEASE_TAG }}
+