fix: cot agent chinese json bug (#18073)

Co-authored-by: huangzhuo <huangzhuo1@xiaomi.com>

api/core/agent/cot_agent_runner.py

                     # action is final answer, return final answer directly
                     try:
                         if isinstance(scratchpad.action.action_input, dict):
-                            final_answer = json.dumps(scratchpad.action.action_input)
+                            final_answer = json.dumps(scratchpad.action.action_input, ensure_ascii=False)
                         elif isinstance(scratchpad.action.action_input, str):
                             final_answer = scratchpad.action.action_input
                         else: