Fixes #3304. Add missing `asyncStart()` to toDart_t02.dart (#3305)

diff --git a/LibTest/js_interop/JSPromiseToFuture/toDart_t02.dart b/LibTest/js_interop/JSPromiseToFuture/toDart_t02.dart
index 57b8d0f..a2b5baf 100644
--- a/LibTest/js_interop/JSPromiseToFuture/toDart_t02.dart
+++ b/LibTest/js_interop/JSPromiseToFuture/toDart_t02.dart
@@ -25,6 +25,7 @@
   ''');
   JSPromise<JSString> promise = globalContext["promise"] as JSPromise<JSString>;
   Future<JSString> future = promise.toDart;
+  asyncStart();
   future.then(
     (v) {
       Expect.fail("The feature should be completed with an error");