[quick-actions] Revert migrating integration tests to NNBD (#3967)

Reverts the quick_action portion of:
"Move integration test to null safety for multiple plugins (#3932)"
(commit a864de2) since it seems to have
broken XCUITests.

packages/quick_actions/quick_actions/example/integration_test/quick_actions_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'package:flutter_test/flutter_test.dart';
 import 'package:integration_test/integration_test.dart';
 import 'package:quick_actions/quick_actions.dart';
@@ -11,7 +12,7 @@ void main() {
 
   testWidgets('Can set shortcuts', (WidgetTester tester) async {
     final QuickActions quickActions = QuickActions();
-    await quickActions.initialize((String shortcutType) => {});
+    await quickActions.initialize(null);
 
     const ShortcutItem shortCutItem = ShortcutItem(
       type: 'action_one',

packages/quick_actions/quick_actions/example/test_driver/integration_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart=2.9
+
 import 'package:integration_test/integration_test_driver.dart';
 
 Future<void> main() => integrationDriver();

packages/quick_actions/quick_actions/pubspec.yaml

@@ -27,6 +27,8 @@ dependencies:
 dev_dependencies:
   flutter_test:
     sdk: flutter
-  mockito: ^5.0.0
+  integration_test:
+    sdk: flutter
+  mockito: ^5.0.0-nullsafety.7
   pedantic: ^1.11.0
   plugin_platform_interface: ^2.0.0