TESTS: Enable DEBUG Logging in Flaky Test (#34091)

* This should surface what errors are thrown on CI
and in org.elasticsearch.transport.RemoteClusterConnection.ConnectHandler#collectRemoteNodes
(the sequence of caught error in the last catch block and moving on to the next seed node
seems to be the only path by which the errors logged in #33756 could come about)
* Relates #33756

server/src/test/java/org/elasticsearch/transport/RemoteClusterConnectionTests.java

@@ -53,6 +53,7 @@
 import org.elasticsearch.mocksocket.MockServerSocket;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.VersionUtils;
+import org.elasticsearch.test.junit.annotations.TestLogging;
 import org.elasticsearch.test.transport.MockTransportService;
 import org.elasticsearch.test.transport.StubbableTransport;
 import org.elasticsearch.threadpool.TestThreadPool;
@@ -834,6 +835,7 @@ public void run() {
         }
     }
 
+    @TestLogging("_root:DEBUG, org.elasticsearch.transport:TRACE")
     public void testCloseWhileConcurrentlyConnecting() throws IOException, InterruptedException, BrokenBarrierException {
         List<DiscoveryNode> knownNodes = new CopyOnWriteArrayList<>();
         try (MockTransportService seedTransport = startTransport("seed_node", knownNodes, Version.CURRENT);