Ensure SyncManager PendingIntent is immutable.

Bug: 154921790
Test: atest SyncManagerTest
Test: atest CtsSyncManagerTest
Change-Id: I88d9a31f49b87e42e5ec759a59e997eedc224396
diff --git a/services/core/java/com/android/server/content/SyncManager.java b/services/core/java/com/android/server/content/SyncManager.java
index 4a1afb2..041bedc 100644
--- a/services/core/java/com/android/server/content/SyncManager.java
+++ b/services/core/java/com/android/server/content/SyncManager.java
@@ -1819,7 +1819,8 @@
         intent.putExtra(Intent.EXTRA_CLIENT_LABEL,
                 com.android.internal.R.string.sync_binding_label);
         intent.putExtra(Intent.EXTRA_CLIENT_INTENT, PendingIntent.getActivityAsUser(context, 0,
-                new Intent(Settings.ACTION_SYNC_SETTINGS), 0, null, UserHandle.of(userId)));
+                new Intent(Settings.ACTION_SYNC_SETTINGS), PendingIntent.FLAG_IMMUTABLE, null,
+                UserHandle.of(userId)));
 
         return intent;
     }