Fix test

Author: JamesNK

src/Servers/Kestrel/test/Interop.FunctionalTests/Http3/Http3RequestTests.cs

@@ -368,7 +368,7 @@ public async Task GET_MultipleRequestsInSequence_ReusedRequestHeaderStrings()
             });
 
             using (var host = builder.Build())
-            using (var client = new HttpClient())
+            using (var client = CreateClient())
             {
                 await host.StartAsync();