Fix #9440, `batchDAO.endOfFlush();` should be called after all executions are ready. (#9441)

oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/storage/PersistenceTimer.java

@@ -136,8 +136,9 @@ public enum PersistenceTimer {
                             .whenComplete(($1, $2) -> executeLatencyTimer.close());
                 }, prepareExecutorService);
             }).toArray(CompletableFuture[]::new));
-        batchDAO.endOfFlush();
+
         future.whenComplete((unused, throwable) -> {
+            batchDAO.endOfFlush();
             allTimer.close();
             if (log.isDebugEnabled()) {
                 log.debug(