[4.5/N] bugfix for quant config in speculative decode (#10007)

Signed-off-by: youkaichao <youkaichao@gmail.com>

vllm/spec_decode/spec_decode_worker.py

@@ -61,6 +61,10 @@ def create_spec_worker(*args, **kwargs) -> "SpecDecodeWorker":
 
     draft_worker_config = copy.deepcopy(vllm_config)
     draft_worker_config.model_config = speculative_config.draft_model_config
+    draft_worker_config.quant_config = VllmConfig._get_quantization_config(
+        draft_worker_config.model_config,
+        vllm_config.load_config,
+    )
     draft_worker_config.parallel_config = speculative_config.draft_parallel_config  # noqa
     # TODO allow draft-model specific load config.