DelegationRule.Dispose() unsets delegation property on the queue (#28342)

* Add disposing pattern

* Stash (destination) urlgroup on a field

* Make test explicit

Author: shirhatti

src/Servers/HttpSys/src/DelegationRule.cs

@@ -13,6 +13,7 @@ namespace Microsoft.AspNetCore.Server.HttpSys
     public class DelegationRule : IDisposable
     {
         private readonly ILogger _logger;
+        private readonly UrlGroup _urlGroup;
         private readonly UrlGroup _sourceQueueUrlGroup;
         private bool _disposed;
         /// <summary>
@@ -32,6 +33,7 @@ internal DelegationRule(UrlGroup sourceQueueUrlGroup, string queueName, string u
             QueueName = queueName;
             UrlPrefix = urlPrefix;
             Queue = new RequestQueue(queueName, UrlPrefix, _logger, receiver: true);
+            _urlGroup = Queue.UrlGroup;
         }
 
         /// <inheritdoc />
@@ -49,7 +51,7 @@ public void Dispose()
                 _sourceQueueUrlGroup.UnSetDelegationProperty(Queue, throwOnError: false);
             }
             catch (ObjectDisposedException) { /* Server may have been shutdown */ }
-            Queue.UrlGroup.Dispose();
+            _urlGroup.Dispose();
             Queue.Dispose();
         }
     }

src/Servers/HttpSys/test/FunctionalTests/DelegateTests.cs

@@ -186,9 +186,11 @@ public async Task UpdateDelegationRuleTest()
 
             var delegationProperty = delegator.Features.Get<IServerDelegationFeature>();
             destination = delegationProperty.CreateDelegationRule(queueName, receiverAddress);
+            // Send a request to ensure the rule is fully active
+            var responseString = await SendRequestAsync(delegatorAddress);
             destination?.Dispose();
             destination = delegationProperty.CreateDelegationRule(queueName, receiverAddress);
-            var responseString = await SendRequestAsync(delegatorAddress);
+            responseString = await SendRequestAsync(delegatorAddress);
             Assert.Equal(_expectedResponseString, responseString);
             destination?.Dispose();
         }