samples: Update schema.py print (#949)

Format string issue

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Fixes #<issue_number_goes_here> 🦕

samples/snippets/schema.py

@@ -727,7 +727,7 @@ def callback(message: pubsub_v1.subscriber.message.Message) -> None:
         # Deserialize the message data accordingly.
         if encoding == "BINARY":
             state.ParseFromString(message.data)
-            print("Received a binary-encoded message:\n{state}")
+            print(f"Received a binary-encoded message:\n{state}")
         elif encoding == "JSON":
             Parse(message.data, state)
             print(f"Received a JSON-encoded message:\n{state}")