insert_select_connection_leak failing

It failed at https://circleci.com/gh/citusdata/citus/110334?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-build-link

```
--- /home/circleci/project/src/test/regress/expected/insert_select_connection_leak.out.modified 2020-03-31 20:20:13.096470573 +0000
+++ /home/circleci/project/build-11/src/test/regress/results/insert_select_connection_leak.out.modified 2020-03-31 20:20:13.100470526 +0000
@@ -64,21 +64,21 @@

-- ROLLBACK
BEGIN;
INSERT INTO target_table SELECT * FROM source_table;
INSERT INTO target_table SELECT * FROM source_table;
ROLLBACK;
SELECT worker_connection_count(:worker_1_port) - :pre_xact_worker_1_connections AS leaked_worker_1_connections,
worker_connection_count(:worker_2_port) - :pre_xact_worker_2_connections AS leaked_worker_2_connections;
leaked_worker_1_connections | leaked_worker_2_connections
-----------------------------+-----------------------------
- 0 | 0
+ 5 | 0
(1 row)

\set VERBOSITY TERSE
```

We need to investigate this.