Disable test ResponseHeadersRead_SynchronizationContextNotUsedByHandl…

…er for WinHttpHandler on Win7/Win81 (#56490)

Disable test ResponseHeadersRead_SynchronizationContextNotUsedByHandler for WinHttpHandler on Win7/Win81
Test types:
- System.Net.Http.Functional.Tests.PlatformHandler_HttpClientHandler_Asynchrony_Test
- System.Net.Http.Functional.Tests.PlatformHandler_HttpClientHandler_Asynchrony_Http2_Test

Disabled test tracked by #54034

src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.Asynchrony.cs

@@ -26,6 +26,11 @@ from contentMode in Enum.GetValues(typeof(LoopbackServer.ContentMode)).Cast<Loop
         [MemberData(nameof(ResponseHeadersRead_SynchronizationContextNotUsedByHandler_MemberData))]
         public async Task ResponseHeadersRead_SynchronizationContextNotUsedByHandler(bool responseHeadersRead, LoopbackServer.ContentMode contentMode)
         {
+            if (IsWinHttpHandler && (PlatformDetection.IsWindows7 || PlatformDetection.IsWindows8x))
+            {   // [ActiveIssue("https://github.com/dotnet/runtime/issues/54034")]
+                return;
+            }
+
             await Task.Run(async delegate // escape xunit's sync ctx
             {
                 await LoopbackServer.CreateClientAndServerAsync(uri =>