Fixing test.

Author: imcarolwang

src/System.Private.ServiceModel/tests/Scenarios/Client/TypedClient/TypedProxyTests.4.0.0.cs

@@ -613,6 +613,11 @@ public static async Task ServiceContract_TypedProxy_Task_Call_AsyncLocal_NonCapt
             await Task.Yield();
 
             // Force a Gen2 GC so that the WeakReference will no longer have the OperationContextExtension as a target.
+            //GC.Collect(2);
+
+            // Force GC and wait for finalizers
+            GC.Collect(2);
+            GC.WaitForPendingFinalizers();
             GC.Collect(2);
 
             // *** VALIDATE *** \\