Quarantine TestUnixDomainSocketWithUrl (#28069)

- see #24608
- add guards with detailed messages to help debug future failures

Author: dougbu

src/Servers/Kestrel/test/FunctionalTests/UnixDomainSocketsTests.cs

@@ -129,6 +129,7 @@ async Task EchoServer(ConnectionContext connection)
 
 #if LIBUV
         [OSSkipCondition(OperatingSystems.Windows, SkipReason = "Libuv does not support unix domain sockets on Windows.")]
+        [QuarantinedTest("https://github.com/dotnet/aspnetcore/issues/28067")]
 #else
         [MinimumOSVersion(OperatingSystems.Windows, WindowsVersions.Win10_RS4)]
 #endif
@@ -186,7 +187,9 @@ public async Task TestUnixDomainSocketWithUrl()
 
                         var httpResponse = Encoding.ASCII.GetString(readBuffer, 0, read);
                         int httpStatusStart = httpResponse.IndexOf(' ') + 1;
+                        Assert.False(httpStatusStart == 0, $"Space not found in '{httpResponse}'.");
                         int httpStatusEnd = httpResponse.IndexOf(' ', httpStatusStart);
+                        Assert.False(httpStatusEnd == -1, $"Second space not found in '{httpResponse}'.");
 
                         var httpStatus = int.Parse(httpResponse.Substring(httpStatusStart, httpStatusEnd - httpStatusStart), CultureInfo.InvariantCulture);
                         Assert.Equal(httpStatus, StatusCodes.Status200OK);