chore: code format model-selector use enum (#22787)

Co-authored-by: 刘江波 <jiangbo721@163.com>

api/core/workflow/nodes/agent/agent_node.py

                             }
                         )
                     value = tool_value
-                if parameter.type == "model-selector":
+                if parameter.type == AgentStrategyParameter.AgentStrategyParameterType.MODEL_SELECTOR:
                     value = cast(dict[str, Any], value)
                     model_instance, model_schema = self._fetch_model(value)
                     # memory config