Set SslOptions.TargetHost to "localhost" in client

Added explicit assignment of SslOptions.TargetHost to "localhost" in the CreateClient method to ensure correct SSL target host during HTTP requests.

Author: ladeak

tests/CHttpServer.Tests/Http3/Http3IntegrationTests.cs

@@ -18,6 +18,7 @@ protected HttpClient CreateClient()
     {
         var handler = new SocketsHttpHandler();
         handler.SslOptions.RemoteCertificateValidationCallback = (message, certificate, chain, sslPolicyErrors) => certificate?.Issuer == "CN=localhost";
+        handler.SslOptions.TargetHost = "localhost";
         return new HttpClient(handler);
     }