Fix testFlushOnInactive (#52275)

We need to reduce the translog sync interval for indices with translog
async setting so that we can have the safe commit in the assertBusy
interval. This is needed since #51905, where we use the local checkpoint
of the safe commit to calculate the number of uncommitted operations of
a translog stats.

Closes #52251
Relates #51905

Author: dnhatn

server/src/test/java/org/elasticsearch/indices/flush/FlushIT.java

@@ -389,6 +389,7 @@ public void testFlushOnInactive() throws Exception {
             .put(IndexingMemoryController.SHARD_INACTIVE_TIME_SETTING.getKey(), randomTimeValue(10, 1000, "ms")).build());
         assertAcked(client().admin().indices().prepareCreate(indexName).setSettings(Settings.builder()
             .put(IndexMetaData.SETTING_NUMBER_OF_SHARDS, 1).put(IndexMetaData.SETTING_NUMBER_OF_REPLICAS, 1)
+            .put(IndexSettings.INDEX_TRANSLOG_SYNC_INTERVAL_SETTING.getKey(), randomTimeValue(200, 500, "ms"))
             .put(IndexService.GLOBAL_CHECKPOINT_SYNC_INTERVAL_SETTING.getKey(), randomTimeValue(50, 200, "ms"))
             .put("index.routing.allocation.include._name", String.join(",", dataNodes))
             .build()));