pgsql: Clean up some misplaced comments in partition_join.sql regressio

Clean up some misplaced comments in partition_join.sql regression test. Also, add a comment explaining a test case. Back-patch to 11 where the regression test was added. Discussion: https://postgr.es/m/CAPmGK15adZPh2B%2BmGUjSOMH%2BH39ogDRWfCfm4G6jncZCAs9V_Q%40mail.gmail.com Branch -- REL_1

pgsql: Clean up some misplaced comments in partition_join.sql regressio

Clean up some misplaced comments in partition_join.sql regression test. Also, add a comment explaining a test case. Back-patch to 11 where the regression test was added. Discussion: https://postgr.es/m/CAPmGK15adZPh2B%2BmGUjSOMH%2BH39ogDRWfCfm4G6jncZCAs9V_Q%40mail.gmail.com Branch -- REL_1

pgsql: Clean up some misplaced comments in partition_join.sql regressio

Clean up some misplaced comments in partition_join.sql regression test. Also, add a comment explaining a test case. Back-patch to 11 where the regression test was added. Discussion: https://postgr.es/m/CAPmGK15adZPh2B%2BmGUjSOMH%2BH39ogDRWfCfm4G6jncZCAs9V_Q%40mail.gmail.com Branch -- maste