Update pg_query version to 4.2.1

pg_query version 4.2.1 contains a fix that we made: https://github.com/pganalyze/pg_query/pull/285, which we need to pull in to solve an issue we are facing: gitlab-org/gitlab!120838 (comment 1391948269)

Since labkit-ruby depends on pg_query version 2.1, we need to change this first, before we can update the gem in gitlab master