Fix issues with subscription cleanup (#8763)

Author: tobias-tengler

src/HotChocolate/Core/src/Execution/Processing/SubscriptionExecutor.Subscription.cs

@@ -123,7 +123,16 @@ public async ValueTask DisposeAsync()
         {
             if (!_disposed)
             {
-                await _sourceStream.DisposeAsync().ConfigureAwait(false);
+                try
+                {
+                    await _sourceStream.DisposeAsync().ConfigureAwait(false);
+                }
+                catch
+                {
+                    // We ignore any errors during disposal, so we can still
+                    // gracefully dispose the subscription scope.
+                }
+
                 _subscriptionScope?.Dispose();
                 _disposed = true;
             }

src/HotChocolate/Fusion-vnext/src/Fusion.Execution/Execution/Nodes/OperationExecutionNode.cs

@@ -414,7 +414,7 @@ public async ValueTask<bool> MoveNextAsync()
 
         public async ValueTask DisposeAsync()
         {
-            if (!_disposed)
+            if (_disposed)
             {
                 return;
             }