test: add big schema openapi test

The io test is marked as pending for now, because the stack size it
requires is too big.

test/io/fixtures.sql

@@ -1,5 +1,8 @@
+\ir big_schema.sql
 \ir db_config.sql
 
+set search_path to public;
+
 CREATE ROLE postgrest_test_anonymous;
 ALTER ROLE :USER SET pgrst.db_anon_role = 'postgrest_test_anonymous';