[Authorize.Net] fix: nest trackData underneath payment node as required

This fixes this remote test error: 
```
RemoteAuthorizeNetTest#test_card_present_purchase_with_track_data_only [test/remote/gateways/remote_authorize_net_test.rb:169]:
<"This transaction has been approved"> expected but was
<"The element 'transactionRequest' in namespace 'AnetApi/xml/v1/schema/AnetApiSchema.xsd' has invalid child element 'trackData' in namespace 'AnetApi/xml/v1/schema/AnetApiSchema.xsd'. List of possible elements expected: 'currencyCode, payment, profile, solution, authCode, refTransId, splitTenderId, order, lineItems, tax, duty, shipping, taxExempt, poNumber, customer, billTo, shipTo, customerIP, cardholderAuthentication, retail, transactionSettings, userFields' in namespace 'AnetApi/xml/v1/schema/AnetApiSchema.xsd'">.
```
The `<trackData>` node simply needs to be nested inside a `<payment>` node.

Please review @girasquid @j-mutter