fix: not logging tx variables and pre-request (#4341)

Addresses the first item on https://github.com/PostgREST/postgrest/issues/3934

test/spec/fixtures/schema.sql

@@ -3843,3 +3843,6 @@ $$ language sql;
 create or replace function test.delete_items_returns_void() returns void as $$
   delete from items;
 $$ language sql;
+
+create function do_nothing() returns void as $_$
+$_$ language sql;