message: Update subscriber benchmarks to track API changes
  CI doesn't check that, but it should...
diff: @@ -11,7 +11,7 @@ use tokio_trace::{field, span, subscriber, Event, Meta};
  struct EnabledSubscriber;
  impl tokio_trace::Subscriber for EnabledSubscriber {
  - fn new_span(&self, span: span::Data) -> span::Id {
  + fn new_span(&self, span: span::Attributes) -> span::Id {
  let _ = span;
  span::Id::from_u64(0)
  }
  @@ -60,8 +60,8 @@ impl tokio_trace::Subscriber for EnabledSubscriber {
  struct AddData(Mutex<Option<span::Data>>);
  impl tokio_trace::Subscriber for AddData {
  - fn new_span(&self, span: span::Data) -> span::Id {
  - *self.0.lock().unwrap() = Some(span);
  + fn new_span(&self, span: span::Attributes) -> span::Id {
  + *self.0.lock().unwrap() = Some(span.into());
  span::Id::from_u64(0)
  }
  