Update durable-functions-external-events.md

Fixed missing `yield` for Python sample code

Author: shibayan

articles/azure-functions/durable/durable-functions-external-events.md

@@ -62,7 +62,7 @@ import azure.functions as func
 import azure.durable_functions as df
 
 def orchestrator_function(context: df.DurableOrchestrationContext):
-    approved = context.wait_for_external_event('Approval')
+    approved = yield context.wait_for_external_event('Approval')
     if approved:
         # approval granted - do the approved action
     else:
@@ -168,7 +168,7 @@ def orchestrator_function(context: df.DurableOrchestrationContext):
     event2 = context.wait_for_external_event('Event2')
     event3 = context.wait_for_external_event('Event3')
 
-    winner = context.task_any([event1, event2, event3])
+    winner = yield context.task_any([event1, event2, event3])
     if winner == event1:
         # ...
     elif winner == event2:
@@ -423,4 +423,4 @@ In this case, the instance ID is hardcoded as *MyInstanceId*.
 > [Learn how to implement error handling](durable-functions-error-handling.md)
 
 > [!div class="nextstepaction"]
-> [Run a sample that waits for human interaction](durable-functions-phone-verification.md)
+> [Run a sample that waits for human interaction](durable-functions-phone-verification.md)