Fix further fallout from EXPLAIN ANALYZE BUFFERS change
c2a4078eb adjusted EXPLAIN ANALYZE to default the BUFFERS to ON. This
(hopefully) fixes the last remaining issue with regression test failures
with -D RELCACHE_FORCE_RELEASE -D CATCACHE_FORCE_RELEASE builds, where
the planner accesses more buffers due to the cold caches.
Discussion: https://postgr.es/m/CAApHDvqLdzgz77JsE-yTki3w9UiKQ-uTMLRctazcu+99-ips3g@mail.gmail.com