Modernize DiagnosticsHandler tests (#53870)

* Modernize DiagnosticsHandler tests

* Address PR feedback

SemaphoreSlim => TCS, Guid => nosuchhost.invalid, Http20 => Http2

src/libraries/System.Net.Http/tests/FunctionalTests/FakeDiagnosticSourceListenerObserver.cs

@@ -71,11 +71,6 @@ public void Enable(Func<string, object, object, bool> writeObserverEnabled)
             _writeObserverEnabled = writeObserverEnabled;
         }
 
-        public void Disable()
-        {
-            _writeObserverEnabled = (name, arg1, arg2) => false;
-        }
-
         private bool IsEnabled(string s, object arg1, object arg2)
         {
             return _writeObserverEnabled.Invoke(s, arg1, arg2);

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

@@ -78,6 +78,9 @@ protected static object GetUnderlyingSocketsHttpHandler(HttpClientHandler handle
 
         protected LoopbackServerFactory LoopbackServerFactory => GetFactoryForVersion(UseVersion, UseQuicImplementationProvider);
 
+        protected static LoopbackServerFactory GetFactoryForVersion(string useVersion, QuicImplementationProvider quicImplementationProvider = null) =>
+            GetFactoryForVersion(Version.Parse(useVersion), quicImplementationProvider);
+
         protected static LoopbackServerFactory GetFactoryForVersion(Version useVersion, QuicImplementationProvider quicImplementationProvider = null)
         {
             return useVersion.Major switch

src/libraries/System.Net.Http/tests/FunctionalTests/SocketsHttpHandlerTest.cs

@@ -141,9 +141,15 @@ public sealed class SocketsHttpHandler_HttpProtocolTests_Dribble : HttpProtocolT
         public SocketsHttpHandler_HttpProtocolTests_Dribble(ITestOutputHelper output) : base(output) { }
     }
 
-    public sealed class SocketsHttpHandler_DiagnosticsTest : DiagnosticsTest
+    public sealed class SocketsHttpHandler_DiagnosticsTest_Http11 : DiagnosticsTest
     {
-        public SocketsHttpHandler_DiagnosticsTest(ITestOutputHelper output) : base(output) { }
+        public SocketsHttpHandler_DiagnosticsTest_Http11(ITestOutputHelper output) : base(output) { }
+    }
+
+    public sealed class SocketsHttpHandler_DiagnosticsTest_Http2 : DiagnosticsTest
+    {
+        public SocketsHttpHandler_DiagnosticsTest_Http2(ITestOutputHelper output) : base(output) { }
+        protected override Version UseVersion => HttpVersion.Version20;
     }
 
     public sealed class SocketsHttpHandler_HttpClient_SelectedSites_Test : HttpClient_SelectedSites_Test