feat(oonirun): improve tests (#915)

See https://github.com/ooni/probe/issues/2184

While there, rename `runtimex.PanicIfFalse` to `runtimex.Assert` (it was about time...)

internal/measurexlite/failure.go

@@ -27,7 +27,7 @@ func NewFailure(err error) *string {
 	if !errors.As(err, &errWrapper) {
 		err := netxlite.NewTopLevelGenericErrWrapper(err)
 		couldConvert := errors.As(err, &errWrapper)
-		runtimex.PanicIfFalse(couldConvert, "we should have an ErrWrapper here")
+		runtimex.Assert(couldConvert, "we should have an ErrWrapper here")
 	}
 	s := errWrapper.Failure
 	if s == "" {