Permit longer chain building fetching for dynamic revocation tests

This is meant to address the flakiness where chain building can time out for very busy CI machines.

The test fixture is already outerloop, so extending the timeout should not adversely affect CI inner loop performance.

src/libraries/System.Security.Cryptography.X509Certificates/tests/RevocationTests/DynamicRevocationTests.cs

@@ -15,7 +15,7 @@ namespace System.Security.Cryptography.X509Certificates.Tests.RevocationTests
     public static partial class DynamicRevocationTests
     {
         // The CI machines are doing an awful lot of things at once, be generous with the timeout;
-        internal static readonly TimeSpan s_urlRetrievalLimit = TimeSpan.FromSeconds(15);
+        internal static readonly TimeSpan s_urlRetrievalLimit = TimeSpan.FromSeconds(30);
 
         private static readonly Oid s_tlsServerOid = new Oid("1.3.6.1.5.5.7.3.1", null);