[google_sign_in] Make the Delegate non-final to allow overriding (#2660)

Make the Delegate non-final to allow overriding. IDelegate is not enough for v2 embedding for GoogleSignIn and 1p auth plugin because activity and activity binding have to be involved. If we keep Delegate as a field for those plugins, make Delegate non-final so that it's easier for tests to override.
diff --git a/packages/google_sign_in/google_sign_in/CHANGELOG.md b/packages/google_sign_in/google_sign_in/CHANGELOG.md
index 9c031f9..dfe674e 100644
--- a/packages/google_sign_in/google_sign_in/CHANGELOG.md
+++ b/packages/google_sign_in/google_sign_in/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 4.4.2
+
+* Android: make the Delegate non-final to allow overriding.
+
 ## 4.4.1
 
 * Android: Move `GoogleSignInWrapper` to a separate class.
diff --git a/packages/google_sign_in/google_sign_in/android/src/main/java/io/flutter/plugins/googlesignin/GoogleSignInPlugin.java b/packages/google_sign_in/google_sign_in/android/src/main/java/io/flutter/plugins/googlesignin/GoogleSignInPlugin.java
index f398721..2913aae 100755
--- a/packages/google_sign_in/google_sign_in/android/src/main/java/io/flutter/plugins/googlesignin/GoogleSignInPlugin.java
+++ b/packages/google_sign_in/google_sign_in/android/src/main/java/io/flutter/plugins/googlesignin/GoogleSignInPlugin.java
@@ -241,7 +241,7 @@
    * completed (either successfully or in error). This class provides no synchronization constructs
    * to guarantee such behavior; callers are responsible for providing such guarantees.
    */
-  public static final class Delegate implements IDelegate, PluginRegistry.ActivityResultListener {
+  public static class Delegate implements IDelegate, PluginRegistry.ActivityResultListener {
     private static final int REQUEST_CODE_SIGNIN = 53293;
     private static final int REQUEST_CODE_RECOVER_AUTH = 53294;
     @VisibleForTesting static final int REQUEST_CODE_REQUEST_SCOPE = 53295;
diff --git a/packages/google_sign_in/google_sign_in/pubspec.yaml b/packages/google_sign_in/google_sign_in/pubspec.yaml
index 94b1e42..0631a66 100644
--- a/packages/google_sign_in/google_sign_in/pubspec.yaml
+++ b/packages/google_sign_in/google_sign_in/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Flutter plugin for Google Sign-In, a secure authentication system
   for signing in with a Google account on Android and iOS.
 homepage: https://github.com/flutter/plugins/tree/master/packages/google_sign_in/google_sign_in
-version: 4.4.1
+version: 4.4.2
 
 flutter:
   plugin: