Update gitlab-labkit & pg_query gems

What does this MR do and why?

Update to pg_query to version 4.2.1 from 2.1

We need to update the version of pg_query as 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: !120838 (comment 1391948269).

Update to gitlab-labkit to version 0.33.0 from 0.32.0

Since gitlab-labkit depends on pg_query version 2.1 currently, labkit was also updated yesterday to use pg_query 4.2.1: gitlab-org/ruby/gems/labkit-ruby!114 (merged), and we have tagged a new version 0.33.0, so we need to update gitlab-labkit too.

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