[webview_flutter] Update sample code. (#4727)

Documentation was updated in app-example file but not in `webview_controller.dart`.   
'output' is a positional parameter now, and `JavascriptMessage` changed to `JavaScriptMessage`

Fixes issue flutter/flutter#132727
diff --git a/packages/webview_flutter/webview_flutter/CHANGELOG.md b/packages/webview_flutter/webview_flutter/CHANGELOG.md
index bca5b63..2f15f13 100644
--- a/packages/webview_flutter/webview_flutter/CHANGELOG.md
+++ b/packages/webview_flutter/webview_flutter/CHANGELOG.md
@@ -1,5 +1,6 @@
-## NEXT
+## 4.2.3
 
+* Fixes the code sample in the dartdocs for `WebViewController.addJavaScriptChannel`.
 * Updates minimum supported SDK version to Flutter 3.7/Dart 2.19.
 
 ## 4.2.2
diff --git a/packages/webview_flutter/webview_flutter/lib/src/webview_controller.dart b/packages/webview_flutter/webview_flutter/lib/src/webview_controller.dart
index f8e4c41..13435ed 100644
--- a/packages/webview_flutter/webview_flutter/lib/src/webview_controller.dart
+++ b/packages/webview_flutter/webview_flutter/lib/src/webview_controller.dart
@@ -266,8 +266,8 @@
   /// ```dart
   /// final WebViewController controller = WebViewController();
   /// controller.addJavaScriptChannel(
-  ///   name: 'Print',
-  ///   onMessageReceived: (JavascriptMessage message) {
+  ///   'Print',
+  ///   onMessageReceived: (JavaScriptMessage message) {
   ///     print(message.message);
   ///   },
   /// );
diff --git a/packages/webview_flutter/webview_flutter/pubspec.yaml b/packages/webview_flutter/webview_flutter/pubspec.yaml
index 645094b..a1c006f 100644
--- a/packages/webview_flutter/webview_flutter/pubspec.yaml
+++ b/packages/webview_flutter/webview_flutter/pubspec.yaml
@@ -2,7 +2,7 @@
 description: A Flutter plugin that provides a WebView widget on Android and iOS.
 repository: https://github.com/flutter/packages/tree/main/packages/webview_flutter/webview_flutter
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+webview%22
-version: 4.2.2
+version: 4.2.3
 
 environment:
   sdk: ">=2.19.0 <4.0.0"