#27338 Adapt test case to supply extension attributes instead of custom attributes

(still not failing with the fix reverted)

Author: amenk

dev/tests/api-functional/testsuite/Magento/Quote/Api/GuestShipmentEstimationWithExtensionAttributesTest.php

@@ -80,11 +80,8 @@ public function testEstimateByExtendedAddress()
                 AddressInterface::CUSTOMER_ADDRESS_ID => $address->getCustomerAddressId(),
                 AddressInterface::SAVE_IN_ADDRESS_BOOK => $address->getSaveInAddressBook(),
 
-                'custom_attributes' => [
-                    [
-                    'attribute_code' =>  'test_attribute',
-                    'value' => 1,
-                    ],
+                'extension_attributes' => [
+                    'test_attribute' => 1
                 ]
             ];