[GraphBolt] PyG example typo fix (#6931)

examples/sampling/pyg/node_classification.py

@@ -224,7 +224,7 @@ def main():
 
         valid_accuracy = evaluate(model, valid_dataloader, device, num_classes)
         print(
-            f"Epoch {epoch}, Train Loss: {train_loss:.4f}, Train Accuracy: {valid_accuracy:.4f}, "
+            f"Epoch {epoch}, Train Loss: {train_loss:.4f}, Train Accuracy: {train_accuracy:.4f}, "
             f"Valid Accuracy: {valid_accuracy:.4f}"
         )
     test_accuracy = evaluate(model, test_dataloader, device, num_classes)