[fix][test] Move ExtensibleLoadManagerCloseTest test group to flaky

Signed-off-by: Zixuan Liu <[email protected]>

Author: nodece

pulsar-broker/src/test/java/org/apache/pulsar/broker/loadbalance/extensions/ExtensibleLoadManagerCloseTest.java

@@ -36,6 +36,7 @@
 import org.testng.annotations.Test;
 
 @Slf4j
+@Test(groups = "flaky")
 public class ExtensibleLoadManagerCloseTest {
 
     private static final String clusterName = "test";