Require feature flag for remote cluster port test (elastic#92955)

Fixes elastic#92943. The test uses a feature flagged setting but does not
`assumeTrue` on the feature flag.

Author: n1v0lg

server/src/internalClusterTest/java/org/elasticsearch/transport/RemoteClusterPortSettingsIT.java

@@ -19,6 +19,8 @@
 public class RemoteClusterPortSettingsIT extends ESIntegTestCase {
 
     public void testDirectlyConfiguringTransportProfileForRemoteClusterWillFailToStartTheNode() {
+        assumeTrue("untrusted remote cluster feature flag must be enabled", TcpTransport.isUntrustedRemoteClusterEnabled());
+
         internalCluster().setBootstrapMasterNodeIndex(0);
 
         final Settings.Builder builder = Settings.builder()