Make sure we wrap all AsyncErrors in ScheduleErrors.

pkg/scheduled_test/lib/src/schedule_error.dart

Index: pkg/scheduled_test/lib/src/schedule_error.dart
diff --git a/pkg/scheduled_test/lib/src/schedule_error.dart b/pkg/scheduled_test/lib/src/schedule_error.dart
index 76d6e009be2980c858b329789fa404b4d86408fa..a985e0da03187425f50bcf043e4369a421f90f8a 100644
--- a/pkg/scheduled_test/lib/src/schedule_error.dart
+++ b/pkg/scheduled_test/lib/src/schedule_error.dart
@@ -30,9 +30,7 @@ class ScheduleError extends AsyncError {
   /// [AsyncError]s and [ScheduleError]s will be preserved.
   factory ScheduleError.from(Schedule schedule, error, {stackTrace,
       AsyncError cause}) {
-    if (error is ScheduleError) {
-      if (schedule == null) schedule = error.schedule;
-    }
+    if (error is ScheduleError) return error;
 
     if (error is AsyncError) {
       // Overwrite the explicit stack trace, because it probably came from a