Move test for BRIN HOT behavior to stats.sql
The test added by
5753d4ee32 relies on statistics collector, and so it
may occasionally fail when the UDP packet gets lost. Some machines may
be susceptible to this, probably depending on load etc.
Move the test to stats.sql, which is known to already have this issue
and people know to ignore it.
Reported-by: Justin Pryzby
Discussion: https://postgr.es/m/CAFp7QwpMRGcDAQumN7onN9HjrJ3u4X3ZRXdGFT0K5G2JWvnbWg%40mail.gmail.com