[fix](autoinc) Fix broker load when target table has autoinc column (#28402)

fe/fe-core/src/main/java/org/apache/doris/load/loadv2/LoadingTaskPlanner.java

@@ -154,6 +154,7 @@ public class LoadingTaskPlanner {
             slotDesc.setIsMaterialized(true);
             slotDesc.setColumn(col);
             slotDesc.setIsNullable(col.isAllowNull());
+            slotDesc.setAutoInc(col.isAutoInc());
             SlotDescriptor scanSlotDesc = descTable.addSlotDescriptor(scanTupleDesc);
             scanSlotDesc.setIsMaterialized(true);
             scanSlotDesc.setColumn(col);