Fix loopback server for H/3

Author: ManickaP

src/libraries/System.Net.Http.WinHttpHandler/tests/FunctionalTests/HttpClientHandlerTestBase.WinHttpHandler.cs

@@ -41,8 +41,10 @@ protected static LoopbackServerFactory GetFactoryForVersion(Version useVersion)
         {
             return useVersion.Major switch
             {
+                1 => Http11LoopbackServerFactory.Singleton,
                 2 => Http2LoopbackServerFactory.Singleton,
-                _ => Http11LoopbackServerFactory.Singleton
+                3 => Http3LoopbackServerFactory.Singleton,
+                _ => throw new InvalidOperationException($"Unexpected HTTP version: {useVersion}");
             };
         }