[Bugfix] fix lora_dtype value type in arg_utils.py (#5398)

Author: c3-ali

vllm/engine/arg_utils.py

@@ -68,7 +68,7 @@ class EngineArgs:
     fully_sharded_loras: bool = False
     lora_extra_vocab_size: int = 256
     long_lora_scaling_factors: Optional[Tuple[float]] = None
-    lora_dtype = 'auto'
+    lora_dtype: str = 'auto'
     max_cpu_loras: Optional[int] = None
     device: str = 'auto'
     ray_workers_use_nsight: bool = False