[MRM-1871] ConcurrentModificationException in DefaultRepositoryProxyConnectors

create a copy to avoid ConcurrentModificationException

archiva-modules/archiva-base/archiva-proxy/src/main/java/org/apache/archiva/proxy/DefaultRepositoryProxyConnectors.java

@@ -1262,7 +1262,7 @@ public class DefaultRepositoryProxyConnectors
         }
 
         Collections.sort( ret, ProxyConnectorOrderComparator.getInstance() );
-        return ret;
+        return new ArrayList<>( ret );
 
     }