Adjust test case to newly introduced shipping method and rates

This change adds newly introduced shipping method 'USPS GroundAdvantage'. EasyPost ShippingRate with 'USPS First' and 'USPS ParcelSelect' services are no longer being added with the newest version of EasyPost.
Additionally, estimated rates for 'USPS Express' and 'USPS Priority' have increased to 28.0 and 7.12 respectively.

Author: JustShah