build arg didn't take

.woodpecker/main.yml

@@ -37,7 +37,7 @@ pipeline:
       - REGISTRY_USER=michael
       - ORGANIZATION=containers
       - REPO=matrix-service-synapse
-      - BUILD_ARGS="PYTHON_VERSION=3.10"
+      - BUILD_ARGS=PYTHON_VERSION=3.10
       - DOCKERFILE=docker/Dockerfile
       - CONTEXT=.
     commands:
@@ -49,7 +49,7 @@ pipeline:
         -t $REGISTRY/$ORGANIZATION/$REPO:$(date +%F)
         -t $REGISTRY/$ORGANIZATION/$REPO:latest
         --pull
-        --build-arg $BUILD_ARGS
+        --build-arg $${BUILD_ARGS}
         -f $${DOCKERFILE}
-        $CONTEXT
+        $${CONTEXT}
       - docker push -a $REGISTRY/$ORGANIZATION/$REPO