chore: alter example to move code inside test function

Co-authored-by: Heitor Lessa <lessa@amazon.co.uk>

Author: Tom McCarthy

docs/utilities/idempotency.md

@@ -814,12 +814,12 @@ To test with [DynamoDB Local](https://docs.aws.amazon.com/amazondynamodb/latest/
 
     import app
 
-    # Create our own Table resource using the endpoint for our DynamoDB Local instance
-    resource = boto3.resource("dynamodb", endpoint_url='http://localhost:8000')
-    table = resource.Table(app.persistence_layer.table_name)
-    app.persistence_layer.table = table
-
     def test_idempotent_lambda():
+        # Create our own Table resource using the endpoint for our DynamoDB Local instance
+        resource = boto3.resource("dynamodb", endpoint_url='http://localhost:8000')
+        table = resource.Table(app.persistence_layer.table_name)
+        app.persistence_layer.table = table
+    
         result = app.handler({'testkey': 'testvalue'}, {})
         assert result['payment_id'] == 12345
     ```