Try to stabilize results of new tuplesort regression test.
It appears that a concurrent autovacuum/autoanalyze run can cause
changes in the plans expected by this test. To prevent that, change
the tables it uses to be temp tables --- there's no need for them
to be permanent, and this should save a few cycles too.
Discussion: https://postgr.es/m/3244.
1576160824@sss.pgh.pa.us