Fix some leaky tests. (#157294)

packages/flutter/test/cupertino/nav_bar_test.dart

@@ -2089,6 +2089,7 @@ void main() {
 
   testWidgets('Large title snaps up to persistent nav bar when partially scrolled over halfway up', (WidgetTester tester) async {
     final ScrollController scrollController = ScrollController();
+    addTearDown(scrollController.dispose);
     const double largeTitleHeight = 52.0;
 
     await tester.pumpWidget(
@@ -2130,6 +2131,7 @@ void main() {
 
   testWidgets('Large title snaps back to extended height when partially scrolled halfway up or less', (WidgetTester tester) async {
     final ScrollController scrollController = ScrollController();
+    addTearDown(scrollController.dispose);
     const double largeTitleHeight = 52.0;
 
     await tester.pumpWidget(
@@ -2170,6 +2172,7 @@ void main() {
 
   testWidgets('Large title and bottom snap up when partially scrolled over halfway up in automatic mode', (WidgetTester tester) async {
     final ScrollController scrollController = ScrollController();
+    addTearDown(scrollController.dispose);
     const double largeTitleHeight = 52.0;
     const double bottomHeight = 100.0;
 
@@ -2228,6 +2231,7 @@ void main() {
 
   testWidgets('Large title and bottom snap down when partially scrolled halfway up or less in automatic mode', (WidgetTester tester) async {
     final ScrollController scrollController = ScrollController();
+    addTearDown(scrollController.dispose);
     const double largeTitleHeight = 52.0;
     const double bottomHeight = 100.0;
 

packages/flutter/test/material/menu_anchor_test.dart

@@ -4667,12 +4667,18 @@ void main() {
       return results;
     }
 
+    late final OverlayEntry overlayEntry;
+    addTearDown((){
+      overlayEntry.remove();
+      overlayEntry.dispose();
+    });
+
     Widget boilerplate() {
       return MaterialApp(
         home: Overlay(
           key: overlayKey,
           initialEntries: <OverlayEntry>[
-            OverlayEntry(
+            overlayEntry = OverlayEntry(
               builder: (BuildContext context) {
                 return Scaffold(
                   body: Center(

packages/flutter/test/widgets/router_test.dart

@@ -41,9 +41,7 @@ void main() {
     expect(find.text('update'), findsOneWidget);
   });
 
-  testWidgets('Router respects update order',
-  experimentalLeakTesting: LeakTesting.settings.withCreationStackTrace(),
-  (WidgetTester tester) async {
+  testWidgets('Router respects update order', (WidgetTester tester) async {
     final SimpleRouteInformationProvider provider = SimpleRouteInformationProvider();
     addTearDown(provider.dispose);
     provider.value = RouteInformation(