[fix][broker] Flaky-test: TopicTransactionBufferTest.testMessagePublishInOrder (#24788)

Signed-off-by: Dream95 <[email protected]>

Author: Dream95

pulsar-broker/src/main/java/org/apache/pulsar/broker/transaction/buffer/impl/TopicTransactionBuffer.java

@@ -232,6 +232,11 @@ public CompletableFuture<TransactionMeta> getTransactionMeta(TxnID txnID) {
         return CompletableFuture.completedFuture(null);
     }
 
+    @VisibleForTesting
+    public void setPublishFuture(CompletableFuture<Position> publishFuture) {
+        this.publishFuture = publishFuture;
+    }
+
     @VisibleForTesting
     public CompletableFuture<Position> getPublishFuture() {
         return publishFuture;
@@ -298,7 +303,7 @@ public CompletableFuture<Position> appendBufferToTxn(TxnID txnId, long sequenceI
                         "Transaction Buffer recover failed, the current state is: " + getState()));
             }
         }).whenComplete(((position, throwable) -> buffer.release()));
-        publishFuture = future;
+        setPublishFuture(future);
         return future;
     }