fix MLTaskState enum serialization errors (opensearch-project#4158)

Signed-off-by: Xun Zhang <[email protected]>

Author: Zhangxunmt

plugin/src/main/java/org/opensearch/ml/task/MLTaskManager.java

@@ -130,8 +130,8 @@ public synchronized void checkMaxBatchJobTask(MLTaskType mlTaskType, Integer max
                 .must(
                     QueryBuilders
                         .boolQuery()
-                        .should(QueryBuilders.termQuery(STATE_FIELD, CREATED))
-                        .should(QueryBuilders.termQuery(STATE_FIELD, RUNNING))
+                        .should(QueryBuilders.termQuery(STATE_FIELD, CREATED.name()))
+                        .should(QueryBuilders.termQuery(STATE_FIELD, RUNNING.name()))
                 );
 
             SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder().query(boolQuery);