test: log message.data for debugging (GoogleCloudPlatform#126)

* test: log message.data for debugging

Flaky test from GoogleCloudPlatform#124 suggests that `message.data` might have been deformed somehow. Adding a logging for the data passed
to help debug next time something goes wrong.

* chore: update for lint

* chore: update message formatting

* chore: remove extra print

* chore: making lint happy

Author: dandhlee

securitycenter/snippets/snippets_notification_receiver.py

@@ -29,7 +29,9 @@ def receive_notifications(project_id, subscription_name):
     # TODO: subscription_name = "your-subscription-name"
 
     def callback(message):
-        print("Received message")
+
+        # Print the data received for debugging purpose if needed
+        print(f"Received message: {message.data}")
 
         notification_msg = NotificationMessage.from_json(message.data)