It's not quite clear why commit 45b980570 has resulted in
some instability here, though interference from concurrent
autovacuum runs seems like a reasonable guess. What is
clear is that the output ordering of the test queries is
underdetermined for no very good reason. Extend the
ORDER BY keys in hopes of fixing the buildfarm.
Discussion: https://postgr.es/m/147499.1600351924@sss.pgh.pa.us
e5209bf37a