[tests] Ignore AcceptSslCertificatesWithCustomValidationCallbackNSUrl…

…SessionHandler - fails due to external factors.

The test fails with:

    [FAIL] AcceptSslCertificatesWithCustomValidationCallbackNSUrlSessionHandler("https://self-signed.badssl.com/") :   Status code was not success
    [FAIL] AcceptSslCertificatesWithCustomValidationCallbackNSUrlSessionHandler("https://wrong.host.badssl.com/") :   Status code was not success

Debugging a bit it seems that these return 404 "Not Found" now, so it seems something changed on badssl.com's side.

We should probably use a different server we control at some point, but filed
an issue for now (#21912).

tests/monotouch-test/System.Net.Http/MessageHandlers.cs

@@ -592,6 +592,7 @@ public void AcceptSslCertificatesServicePointManager (Type handlerType)
 		}
 
 #if NET
+		[Ignore ("https://github.com/xamarin/xamarin-macios/issues/21912")]
 		[TestCase ("https://self-signed.badssl.com/")]
 		[TestCase ("https://wrong.host.badssl.com/")]
 		public void AcceptSslCertificatesWithCustomValidationCallbackNSUrlSessionHandler (string url)