docs: fix typo in get_common_metadata.py sample (#224)

The print statement in the print_get_metadata_response was printing the custom definition status of a dimension when it was supposed to be printing information about the custom definition status of a metric

Co-authored-by: Anthonios Partheniou <partheniou@google.com>

packages/google-analytics-data/samples/snippets/get_common_metadata.py

@@ -61,7 +61,7 @@ def print_get_metadata_response(response):
     for metric in response.metrics:
         print("METRIC")
         print(f"{metric.api_name} ({metric.ui_name}): {metric.description}")
-        print(f"custom_definition: {dimension.custom_definition}")
+        print(f"custom_definition: {metric.custom_definition}")
         if metric.expression:
             print(f"Expression: {metric.expression}")