Flaky test: Fix recover_prepared_transactions (#3205)

Failed test: https://app.circleci.com/jobs/github/citusdata/citus/35994

We now always take a new connection

src/test/regress/expected/failure_ddl.out

@@ -4,6 +4,7 @@
 --    Replication factor, 1PC-2PC, sequential-parallel modes
 -- 
 CREATE SCHEMA ddl_failure;
+SET citus.force_max_query_parallelization TO ON;
 SET search_path TO 'ddl_failure';
 -- do not cache any connections
 SET citus.max_cached_conns_per_worker TO 0;

src/test/regress/sql/failure_ddl.sql

@@ -7,6 +7,7 @@
 
 CREATE SCHEMA ddl_failure;
 
+SET citus.force_max_query_parallelization TO ON;
 SET search_path TO 'ddl_failure';
 
 -- do not cache any connections