Revert "Removes async examples tests"

This reverts commit ce0f781.

Author: elena-kolevska

tox.ini

@@ -51,6 +51,7 @@ commands =
     ./validate.sh error_handling
     ./validate.sh pubsub-simple
     ./validate.sh pubsub-streaming
+    ./validate.sh pubsub-streaming-async
     ./validate.sh state_store
     ./validate.sh state_store_query
     ./validate.sh secret_store