[Flaky-test]: Fix MLTransactionMetadataStoreTest.testInitTransactionR…

…eader fails sporadically (apache#14532)

### Motivation

apache#14525 

When update states is `TxnStatus.COMMITTED`,  Not correctly `completableFuture.complete`.

### Modifications
- When update states is `TxnStatus.COMMITTED`, Add return to ending. Avoid direct calls `completableFuture.complete` from other logic.

### Documentation
- [x ] `no-need-doc`

pulsar-transaction/coordinator/src/main/java/org/apache/pulsar/transaction/coordinator/impl/MLTransactionMetadataStore.java

@@ -393,6 +393,7 @@ public CompletableFuture<Void> updateTxnStatus(TxnID txnID, TxnStatus newStatus,
                                 txnMetaMap.remove(txnID.getLeastSigBits());
                                 completableFuture.complete(null);
                             });
+                            return;
                         }
                         completableFuture.complete(null);
                     } catch (InvalidTxnStatusException e) {