Fixed leak and removed no-shuffle tag in scheduler_test.dart (#88423)

Co-authored-by: Alexander Dahlberg <alexander.dahlberg@sigma.se>

This PR fixed the problem that has prevented scheduler_test.dart being shuffled. Part of #85160.

One test schedules a task, but events are locked so the scheduled task does not execute and this messes up other tests.
This PR adds a teardown that executes the scheduled task after the test, when events are unlocked.

packages/flutter/test/scheduler/scheduler_test.dart

@@ -2,12 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// TODO(gspencergoog): Remove this tag once this test's state leaks/test
-// dependencies have been fixed.
-// https://github.com/flutter/flutter/issues/85160
-// Fails with "flutter test --test-randomize-ordering-seed=123"
-@Tags(<String>['no-shuffle'])
-
 import 'dart:async';
 import 'dart:ui' show window;
 
@@ -140,6 +134,10 @@ void main() {
     for (final VoidCallback timer in timerQueueTasks) {
       timer();
     }
+
+    // As events are locked, make scheduleTask execute after the test or it
+    // will execute during following tests and risk failure.
+    addTearDown(() => scheduler.handleEventLoopCallback());
   });
 
   test('Flutter.Frame event fired', () async {