fix broken qwen3_8b config (meta-pytorch#450)

Author: casteryh

apps/grpo/qwen3_8b.yaml

@@ -29,7 +29,7 @@ dataset:
 # Policy configuration
 policy:
   engine_args:  # https://docs.vllm.ai/en/v0.10.0/api/vllm/engine/arg_utils.html#vllm.engine.arg_utils.EngineArgs
-    model: /mnt/wsfuse/teamforge/hf_artifacts/qwen3_8b
+    model: ${model}
     tensor_parallel_size: 2
     pipeline_parallel_size: 1
     enforce_eager: false