[fix][test] Fix the flaky tests of ManagedLedgerImplUtilsTest (apache#22611)

Author: codelipenghui

managed-ledger/src/test/java/org/apache/bookkeeper/mledger/util/ManagedLedgerImplUtilsTest.java

@@ -21,6 +21,7 @@
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.testng.Assert.assertEquals;
 import java.nio.charset.StandardCharsets;
+import java.util.concurrent.TimeUnit;
 import java.util.function.Predicate;
 import lombok.extern.slf4j.Slf4j;
 import org.apache.bookkeeper.mledger.Entry;
@@ -41,6 +42,8 @@ public void testGetLastValidPosition() throws Exception {
 
         ManagedLedgerConfig managedLedgerConfig = new ManagedLedgerConfig();
         managedLedgerConfig.setMaxEntriesPerLedger(maxEntriesPerLedger);
+        managedLedgerConfig.setRetentionSizeInMB(10);
+        managedLedgerConfig.setRetentionTime(5, TimeUnit.MINUTES);
         ManagedLedger ledger = factory.open("testReverseFindPositionOneByOne", managedLedgerConfig);
 
         String matchEntry = "match-entry";