[shared_preferences]Fix : SetState returning future (#8398)

This pull request includes a change to the `SharedPreferencesDemoState` class in the `main.dart` file. The change improves the way the external counter value is fetched and updated in the state.

* [`packages/shared_preferences/shared_preferences/example/lib/main.dart`](diffhunk://#diff-6e8eaf30aa7259bf259f36e9c2057d82498b436c508f202521b4f8808788c15bL59-R61): Refactored the `_getExternalCounter` method to fetch the external counter value before calling `setState`, ensuring that asynchronous operations are handled correctly.

The issue was : 
```
 FlutterError (setState() callback argument returned a Future.
The setState() method on SharedPreferencesDemoState#1acdd(lifecycle state: created) was called with a closure or method that returned a Future. Maybe it is marked as "async".
Instead of performing asynchronous work inside a call to setState(), first execute the work (without updating the widget state), and then synchronously update the state inside a call to setState().)
```

packages/shared_preferences/shared_preferences/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.5.2
+
+* Fixes `setState` returning `Future` on `example/main.dart` error in example code.
+
 ## 2.5.1
 
 * Exposes `SharedPreferencesOptions`.

packages/shared_preferences/shared_preferences/example/lib/main.dart

@@ -59,8 +59,9 @@ class SharedPreferencesDemoState extends State<SharedPreferencesDemo> {
   /// or via some native system.
   Future<void> _getExternalCounter() async {
     final SharedPreferencesAsync prefs = SharedPreferencesAsync();
-    setState(() async {
-      _externalCounter = (await prefs.getInt('externalCounter')) ?? 0;
+    final int externalCounter = (await prefs.getInt('externalCounter')) ?? 0;
+    setState(() {
+      _externalCounter = externalCounter;
     });
   }
 

packages/shared_preferences/shared_preferences/pubspec.yaml

@@ -3,7 +3,7 @@ description: Flutter plugin for reading and writing simple key-value pairs.
   Wraps NSUserDefaults on iOS and SharedPreferences on Android.
 repository: https://github.com/flutter/packages/tree/main/packages/shared_preferences/shared_preferences
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+shared_preferences%22
-version: 2.5.1
+version: 2.5.2
 
 environment:
   sdk: ^3.5.0