Release 3.47 (#2879)

Minor updates for release 3.47

## 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 have added sample code updates to the [changelog].
- [x] I updated/added relevant documentation (doc comments with `///`).


If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Style-guide-for-Flutter-repo.md
[CLA]: https://cla.developers.google.com/
[Discord]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Chat.md
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md
[changelog]: ../CHANGELOG.md

---------

Co-authored-by: Parker Lougheed <parlough@gmail.com>

cupertino_gallery/lib/widgets/checkbox_page.dart

@@ -17,7 +17,7 @@ class _CheckboxPageState extends State<CheckboxPage> {
       child: Center(
         child: CupertinoCheckbox(
           value: _value,
-          onChanged: (bool? value) {
+          onChanged: (value) {
             setState(() {
               _value = value!;
             });