Fix missing using in Http3TimeoutTests. (#43312)

Co-authored-by: Aditya Mandaleeka <[email protected]>

Author: github-actions[bot]

src/Servers/Kestrel/test/InMemory.FunctionalTests/Http3/Http3TimeoutTests.cs

@@ -5,6 +5,7 @@
 using Microsoft.AspNetCore.Connections;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Server.Kestrel.Core.Features;
+using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http3;
 using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure;
 using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.Logging;