Intermittent test plan change in "privileges" test on BF animal prion

Hello,

Two recent failures show plan changes in RLS queries on master.  Based
on nearby comments, the choice plan is being used to verify access (or
lack of access) to row estimates, so I guess that means something
could be amiss here.  (Or it could be due to the dropped UDP flaky
stats problem, but then why in the same place twice, and why twice in
a week, only on master, and not for months before that?)

https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=prion&dt=2020-06-08%2002%3A58%3A03
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=prion&dt=2020-06-06%2003%3A18%3A03