workflows: fix workflow

.gitea/workflows/build.yaml

@@ -58,6 +58,10 @@ jobs:
           username: ${{ secrets.DOCKER_USERNAME }}
           password: ${{ secrets.DOCKER_PASSWORD }}
 
+      - name: Generate timestamp
+        id: timestamp
+        run: echo "timestamp=$(date +%Y%m%d%H%M%S)" >> $GITEA_OUTPUT
+
       - name: Build Docker image
         uses: docker/build-push-action@v5
         with: