distributed hypertable: unexpected child node of Append or MergeAppend: 60

[akuzm]

 timescaledb │ 2.5.0-dev │ public     │ Enables scalable inserts and complex queries for time-series data
 PostgreSQL 13.4 on x86_64-pc-linux-gnu, compiled by Ubuntu clang version 13.0.0-++20210924062554+d7b669b3a303-1~exp1~20210924163351.114, 64-bit


create table ttt(time timestamptz, series int, value float);
select create_distributed_hypertable('ttt', 'time', partitioning_column => 'series');
insert into ttt select now() + (interval '1 minute') * (random() * 10 + x), x, random() * x from generate_series(1, 1000) x;
explain select * from ttt where now() < now();
ERROR:  unexpected child node of Append or MergeAppend: 60

AsyncAppend can't handle a Result node that is generated on the remote side for a constant true/false qual.

Somewhat related to this one: #3598