Fix ResponseMCPCallArgumentsDeltaEvent type

Author: karpetrosyan

openapi.yaml

@@ -37890,8 +37890,8 @@ components:
         type:
           type: string
           enum:
-            - response.mcp_call.arguments_delta
-          description: The type of the event. Always 'response.mcp_call.arguments_delta'.
+            - response.mcp_call.arguments.delta
+          description: The type of the event. Always 'response.mcp_call.arguments.delta'.
           x-stainless-const: true
         output_index:
           type: integer