Potential fix for code scanning alert no. 71: Nested 'if' statements can be combined

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Author: vb2ae

src/Caliburn.Micro.Platform/Platforms/Xamarin.Forms/AttachedCollection.cs

@@ -55,9 +55,8 @@ protected virtual void OnItemAdded(BindableObject item) {
         /// </summary>
         /// <param name="item">The item that was removed.</param>
         protected virtual void OnItemRemoved(BindableObject item) {
-            if (item is IAttachedObject) {
-                if (((IAttachedObject) item).AssociatedObject != null)
-                    ((IAttachedObject) item).Detach();
+            if (item is IAttachedObject && ((IAttachedObject) item).AssociatedObject != null) {
+                ((IAttachedObject) item).Detach();
             }
         }