test(sdk-core): use supported Sinon assertions

Replace unavailable Sinon assert helpers with the assertion style used by
sdk-core tests and supported by the repository's Sinon version.

WEB-000
PT-000000

Author: mmcshinsky-bitgo

modules/sdk-core/test/unit/bitgo/trading/network/network.test.ts

@@ -100,7 +100,8 @@ describe('TradingNetwork', function () {
         nonce: prepared.nonce,
       })
     );
-    sinon.assert.calledOnceWithExactly(tradingAccount.signPayload, {
+    tradingAccount.signPayload.calledOnce.should.be.true();
+    tradingAccount.signPayload.firstCall.args[0].should.deepEqual({
       payload: prepared.payload,
       walletPassphrase: undefined,
     });