[tests] Mark ProxyTest as Inconclusive on network failure

[jonathanpeppers]

Summary

Mark ProxyTest.QuoteInvalidQuoteUrlsShouldWork as Assert.Inconclusive() on network failure instead of failing the test. This matches the existing pattern used in SslTest and other network-dependent tests.

Problem

The test fails when DNS resolution is unavailable on the test machine:

System.Net.WebException : hostname nor servname provided, or not known (www.msftconnecttest.com:80)
----> System.Net.Http.HttpRequestException : hostname nor servname provided, or not known (www.msftconnecttest.com:80)
----> System.Net.Sockets.SocketException : hostname nor servname provided, or not known

 at System.Net.HttpWebRequest.GetResponse()
 at System.NetTests.ProxyTest.QuoteInvalidQuoteUrlsShouldWork()
 at System.Reflection.DynamicInvokeInfo.Invoke(Object, IntPtr, Object[], BinderBundle, Boolean)
--HttpRequestException
 at System.Net.Http.HttpConnectionPool.<ConnectToTcpHostAsync>d__54.MoveNext()
--- End of stack trace from previous location ---
 at System.Net.Http.HttpConnectionPool.<ConnectAsync>d__53.MoveNext()
--- End of stack trace from previous location ---
 at System.Net.Http.HttpConnectionPool.<CreateHttp11ConnectionAsync>d__82.MoveNext()
--- End of stack trace from previous location ---
 at System.Net.Http.HttpConnectionPool.<InjectNewHttp11ConnectionAsync>d__81.MoveNext()
--- End of stack trace from previous location ---
 at System.Threading.Tasks.TaskCompletionSourceWithCancellation`1.WaitWithCancellation(CancellationToken)
 at System.Net.Http.HttpConnectionPool.<SendWithVersionDetectionAndRetryAsync>d__52.MoveNext()
--- End of stack trace from previous location ---
 at System.Net.Http.RedirectHandler.<SendAsync>d__4.MoveNext()
--- End of stack trace from previous location ---
 at System.Net.Http.HttpMessageHandlerStage.Send(HttpRequestMessage, CancellationToken)
 at System.Net.Http.SocketsHttpHandler.Send(HttpRequestMessage, CancellationToken)
 at System.Net.Http.HttpClient.Send(HttpRequestMessage, HttpCompletionOption, CancellationToken)
 at System.Net.HttpWebRequest.SendRequest(Boolean, HttpContent)
 at System.Net.HttpWebRequest.<HandleResponse>d__201.MoveNext()
--- End of stack trace from previous location ---
 at System.Net.HttpWebRequest.GetResponse()
--SocketException
 at System.Net.Dns.GetHostEntryOrAddressesCore(String, Boolean, AddressFamily, Nullable`1)
 at System.Net.Dns.GetHostAddresses(String, AddressFamily)
 at System.Net.HttpWebRequest.<>c__DisplayClass224_0.<<CreateHttpClient>b__1>d.MoveNext()
--- End of stack trace from previous location ---
 at System.Net.Http.HttpConnectionPool.<ConnectToTcpHostAsync>d__54.MoveNext()

Fix

Wrap the test body in a try/catch that catches WebException with ConnectFailure, NameResolutionFailure, or Timeout status and calls Assert.Inconclusive().

[Copilot]

Pull request overview

This PR adjusts a flaky Mono.Android-Tests network test so transient connectivity problems on the test machine no longer fail the suite outright. It targets System.Net test stability rather than product/runtime behavior.

Changes:

• Wraps ProxyTest.QuoteInvalidQuoteUrlsShouldWork() in a try/catch.
• Treats ConnectFailure, NameResolutionFailure, and Timeout WebExceptions as non-failures.
• Reports those transient failures via an NUnit non-passing result instead of a hard test failure.