fix(webconnectivity): pass TestHelpers to measurement (#736)

* Passed the TestHelpers field to RunAsyc and MeasureAsync. This reflects the test_helpers in the measurement.

* Spec already contains the correct output.

See  https://github.com/ooni/probe/issues/2073

Co-authored-by: decfox <decfox>

internal/engine/experiment.go

@@ -131,6 +131,7 @@ func (eaw *experimentAsyncWrapper) RunAsync(
 			Input:              measurement.Input,
 			MeasurementRuntime: stop.Sub(start).Seconds(),
 			TestKeys:           measurement.TestKeys,
+			TestHelpers:        measurement.TestHelpers,
 		}
 	}()
 	return out, nil
@@ -180,6 +181,7 @@ func (e *Experiment) MeasureAsync(
 			measurement.Extensions = tk.Extensions
 			measurement.Input = tk.Input
 			measurement.MeasurementRuntime = tk.MeasurementRuntime
+			measurement.TestHelpers = tk.TestHelpers
 			measurement.TestKeys = tk.TestKeys
 			if err := measurement.Scrub(e.session.ProbeIP()); err != nil {
 				// If we fail to scrub the measurement then we are not going to