[JBPM-10194] Fix TASK_AVG_DURATION query for postgres (#2331)

jbpm-human-task/jbpm-human-task-audit/src/main/java/org/jbpm/services/task/assignment/impl/TotalCompletionTimeLoadCalculator.java

@@ -50,7 +50,7 @@ public class TotalCompletionTimeLoadCalculator extends AbstractLoadCalculator {
 			+ "select new org.jbpm.services.task.assignment.impl.TaskAverageDuration(avg(bts.duration),t.taskData.deploymentId,t.taskData.processId,bts.taskName) "
 			+ "from BAMTaskSummaryImpl bts left join TaskImpl t on (bts.taskId = t.id) "
 			+ "where (bts.duration is not null) and t.taskData.processId = :procid and t.taskData.deploymentId = :depid and t.name = :taskname "
-			+ "group by t.taskData.deploymentId, t.taskData.processId, t.name";
+			+ "group by t.taskData.deploymentId, t.taskData.processId, t.name, bts.taskName";
 
 	/**
 	 * Initialize the cache