[fix](Nereids) adjust nullable for set operation may cause IndexOutOfBound (#35588)

after we refactor set oepration, let it has projection ability, its
output size may diff with its child's output size. so we should use it
output size as nullable flag list size to ensure it has same size with
set operation's output.

fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/AdjustNullable.java

@@ -168,7 +168,7 @@ public class AdjustNullable extends DefaultPlanRewriter<Map<ExprId, Slot>> imple
         ImmutableList.Builder<List<SlotReference>> newChildrenOutputs = ImmutableList.builder();
         List<Boolean> inputNullable = null;
         if (!setOperation.children().isEmpty()) {
-            inputNullable = setOperation.child(0).getOutput().stream()
+            inputNullable = setOperation.getRegularChildOutput(0).stream()
                     .map(ExpressionTrait::nullable).collect(Collectors.toList());
             for (int i = 0; i < setOperation.arity(); i++) {
                 List<Slot> childOutput = setOperation.child(i).getOutput();