Fix AgentTurnResponseStreamChunk return type

Author: dltn

Sources/LlamaStackClient/openapi.yaml

@@ -2669,7 +2669,7 @@ paths:
       responses:
         '200':
           content:
-            application/json:
+            text/event-stream:
               schema:
                 $ref: '#/components/schemas/AgentTurnResponseStreamChunk'
           description: OK