columnar_indexes failing in my local environment

```
diff -dU10 -w /home/maryxu/pgcodebase/citus/src/test/regress/expected/columnar_indexes.out /home/maryxu/pgcodebase/citus/src/test/regress/results/columnar_indexes.out
--- /home/maryxu/pgcodebase/citus/src/test/regress/expected/columnar_indexes.out.modified 2022-02-03 11:06:48.368151570 -0800
+++ /home/maryxu/pgcodebase/citus/src/test/regress/results/columnar_indexes.out.modified 2022-02-03 11:06:48.408151570 -0800
@@ -589,25 +589,21 @@
SET LOCAL max_parallel_workers_per_gather = 4;
create index on events (event_id);
COMMIT;
CREATE TABLE pending_index_scan(i INT UNIQUE) USING columnar;
BEGIN;
INSERT INTO pending_index_scan SELECT generate_series(1,100);
-- test index scan when there are pending writes
SET LOCAL enable_seqscan TO OFF;
SET LOCAL columnar.enable_custom_scan TO OFF;
SELECT COUNT(*)=100 FROM pending_index_scan ;
- ?column?
----------------------------------------------------------------------
- t
-(1 row)
-
+ERROR: variable not found in subplan target list
COMMIT;
-- show that we don't flush single-tuple stripes due to aborted writes ...
create table uniq(i int unique) using columnar;
-- a) when table has a unique:
begin;
insert into uniq select generate_series(1,100);
-- i) abort before flushing
rollback;
insert into uniq select generate_series(1,100);
SELECT COUNT(*)=1 FROM columnar.stripe cs
@@ -615,25 +611,21 @@
?column?
----------
t
(1 row)

TRUNCATE uniq;
begin;
insert into uniq select generate_series(1,100);
-- ii) abort after flushing
SELECT count(*) FROM uniq;
- count
----------------------------------------------------------------------
- 100
-(1 row)
```