Fix sporadically failing PreAuthenticate test on WinHttpHandler (#28226)

The PreAuthenticate_FirstRequestNoHeader_SecondRequestVariousStatusCodes_ThirdRequestPreauthenticates tests a bunch of status codes, some of which are sporadically failing in CI with WinHttpHandler.  According to the RFC, several of these status codes require that there not be a response body, but the test is sending one, and it would seem there are then race conditions that are causing WinHttp to fail here and there for these status codes, e.g. 204 and 304.  This just fixes the test to not send a body.

Author: stephentoub

src/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Authentication.cs

@@ -326,26 +326,26 @@ await LoopbackServer.CreateClientAndServerAsync(async uri =>
                 using (var client = new HttpClient(handler))
                 {
                     client.DefaultRequestHeaders.ConnectionClose = true; // for simplicity of not needing to know every handler's pooling policy
-                        handler.PreAuthenticate = true;
+                    handler.PreAuthenticate = true;
                     handler.Credentials = s_credentials;
                     client.DefaultRequestHeaders.ExpectContinue = false;
 
                     using (HttpResponseMessage resp = await client.GetAsync(uri))
                     {
                         Assert.Equal(statusCode, resp.StatusCode);
                     }
-                    Assert.Equal("hello world 2", await client.GetStringAsync(uri));
+                    Assert.Equal("hello world", await client.GetStringAsync(uri));
                 }
             },
             async server =>
             {
                 List<string> headers = await server.AcceptConnectionSendResponseAndCloseAsync(HttpStatusCode.Unauthorized, AuthResponse);
                 Assert.All(headers, header => Assert.DoesNotContain("Authorization", header));
 
-                headers = await server.AcceptConnectionSendResponseAndCloseAsync(statusCode, content: "hello world 1");
+                headers = await server.AcceptConnectionSendResponseAndCloseAsync(statusCode);
                 Assert.Contains(headers, header => header.Contains("Authorization"));
 
-                headers = await server.AcceptConnectionSendResponseAndCloseAsync(HttpStatusCode.OK, content: "hello world 2");
+                headers = await server.AcceptConnectionSendResponseAndCloseAsync(HttpStatusCode.OK, content: "hello world");
                 Assert.Contains(headers, header => header.Contains("Authorization"));
             });
         }