Remove call to MulticastDelegate.op_Equality

Author: Sergio0694

CommunityToolkit.Mvvm.SourceGenerators/EmbeddedResources/ObservableObject.cs

@@ -427,7 +427,7 @@ private bool SetPropertyAndNotifyOnCompletion<TTask>(ITaskNotifier<TTask> taskNo
 
         if (isAlreadyCompletedOrNull)
         {
-            if (callback != null)
+            if ((object?)callback != null)
             {
                 callback(newValue);
             }
@@ -450,7 +450,7 @@ async void MonitorTask()
                 OnPropertyChanged(propertyName);
             }
 
-            if (callback != null)
+            if ((object?)callback != null)
             {
                 callback(newValue);
             }