Update for Flutter 3.10 beta (#1746)

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [ ] All existing and new tests are passing.

---------

Co-authored-by: David Iglesias <ditman@gmail.com>
Co-authored-by: Mark Thompson <2554588+MarkTechson@users.noreply.github.com>
Co-authored-by: John Ryan <ryjohn@google.com>

platform_channels/test/src/add_pet_details_test.dart

@@ -11,15 +11,14 @@ void main() {
   group('AddPetDetails tests', () {
     var petList = <Map>[];
 
-    setUpAll(() {
-      const BasicMessageChannel<dynamic>(
-              'jsonMessageCodecDemo', JSONMessageCodec())
-          .setMockMessageHandler((dynamic message) async {
-        petList.add(message as Map);
-      });
-    });
-
     testWidgets('Enter pet details', (tester) async {
+      tester.binding.defaultBinaryMessenger.setMockDecodedMessageHandler(
+        const BasicMessageChannel<dynamic>(
+            'jsonMessageCodecDemo', JSONMessageCodec()),
+        (dynamic message) async {
+          petList.add(message as Map);
+        },
+      );
       var router = app.router('/petListScreen/addPetDetails');
       await tester.pumpWidget(
         MaterialApp.router(