fix sql exception in pgsql (#6576)

Co-authored-by: caishunfeng <534328519@qq.com>

dolphinscheduler-dao/src/main/resources/org/apache/dolphinscheduler/dao/mapper/WorkFlowLineageMapper.xml

@@ -31,7 +31,7 @@
 
     <select id="queryWorkFlowLineageByCode" resultType="org.apache.dolphinscheduler.dao.entity.WorkFlowLineage">
         select tepd.code as work_flow_code,tepd.name as work_flow_name,
-               "" as source_work_flow_code,
+               '' as source_work_flow_code,
                 tepd.release_state as work_flow_publish_status,
                 tes.start_time as schedule_start_time,
                 tes.end_time as schedule_end_time,
@@ -44,7 +44,7 @@
 
     <select id="queryWorkFlowLineageByLineage" resultType="org.apache.dolphinscheduler.dao.entity.WorkFlowLineage">
         select tepd.code as work_flow_code,tepd.name as work_flow_name,
-               "" as source_work_flow_code,
+               '' as source_work_flow_code,
                 tepd.release_state as work_flow_publish_status,
                 tes.start_time as schedule_start_time,
                 tes.end_time as schedule_end_time,