Repro: https://codesandbox.io/s/fast-water-4i4jb

Notice the flash. I'd expect `suspended` to be `true` during the high pri render.
if (childrenIterator) {
            let step = childrenIterator.next();
            let i = 0;
            for (; !step.done; step = childrenIterator.next()) {
              if (!validateSuspenseListNestedChild(step.value, i)) {
                return;
              }
              i++;
            }
          }
        } else {
          console.error(
            'A single row was passed to a <SuspenseList revealOrder="%s" />. ' +
              'This is not useful since it needs multiple rows. ' +
              'Did you mean to pass multiple children or an array?',
            revealOrder,
          );
        }
      }
    }
  }
}
function initSuspenseListRenderState(
  workInProgress: Fiber,
  : boolean,
  : null | Fiber,
  ContentRow: null | Fiber,
  Mode: SuspenseListTailMode,
  EffectBeforeRendering: null | Fiber,
): void {