Commit bf6c614a broke the sepgsql test
due to a new invocation of the function access hook during grouping
equal initialization.

The new behaviour seems at least as correct as the old one, so try
adapt the tests. As I've no working sepgsql setup here, this is just
going from buildfarm results.

Author: Andres Freund
Discussion: https://postgr.es/m/20180217000337.lfsdvro3l6ccsksp@alap3.anarazel.de