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>

form_app/lib/src/sign_in_http.dart

@@ -85,13 +85,11 @@ class _SignInHttpDemoState extends State<SignInHttpDemo> {
                           body: json.encode(formData.toJson()),
                           headers: {'content-type': 'application/json'});
 
-                      if (result.statusCode == 200) {
-                        _showDialog('Successfully signed in.');
-                      } else if (result.statusCode == 401) {
-                        _showDialog('Unable to sign in.');
-                      } else {
-                        _showDialog('Something went wrong. Please try again.');
-                      }
+                      _showDialog(switch (result.statusCode) {
+                        200 => 'Successfully signed in.',
+                        401 => 'Unable to sign in.',
+                        _ => 'Something went wrong. Please try again.'
+                      });
                     },
                   ),
                 ].expand(

form_app/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: "none"
 version: 1.0.0+1
 
 environment:
-  sdk: '>=2.19.5 <4.0.0'
+  sdk: ^3.0.0-0
 
 dependencies:
   flutter: