Fix GUCs for select_parallel regression test

max_parallel_workers_per_gather = 0 breaks new checks in select_parallel
regression test, see the commit adc28d01e98bdfaf9720d363447124d22565620a (Allow
adjusting session_authorization and role in parallel workers.) in PostgreSQL 12.
So use PGOPTIONS as done in other aqo versions. E.g. see the commit
f84caae (One more step towards improving the
AQO regression tests stability.) in the stable13 branch.

Makefile

@@ -23,6 +23,11 @@ REGRESS =	aqo_disabled \
 			gucs
 endif
 
+# Set default values of some gucs to be stable on custom settings during
+# a kind of installcheck
+PGOPTIONS = --max_parallel_workers_per_gather=0
+export PGOPTIONS
+
 fdw_srcdir = $(top_srcdir)/contrib/postgres_fdw
 PG_CPPFLAGS += -I$(libpq_srcdir) -I$(fdw_srcdir)
 EXTRA_REGRESS_OPTS=--temp-config=$(top_srcdir)/$(subdir)/conf.add

conf.add

@@ -1,3 +1,2 @@
 autovacuum = off
 shared_preload_libraries = 'postgres_fdw, aqo'
-max_parallel_workers_per_gather = 0