Update pg_query to v2

What does this MR do?

This updates pg_query to v2 along with dependencies:

1. gitlab-labkit: 0.16.2 => 0.17.1 (https://gitlab.com/gitlab-org/labkit-ruby/-/releases#v0.17.1 - includes upgrade to pg_query v2, too)
2. google-protobuf: 3.14.0 => 3.15.5 (dependency for labkit: https://github.com/protocolbuffers/protobuf/tree/master/ruby)

google-protobuf changes

• pg_query needs protobuf 3.15: https://github.com/pganalyze/pg_query/blob/main/pg_query.gemspec#L28

• Commit: https://github.com/pganalyze/pg_query/commit/ed3a86d78a87653c5e370c2ec9cc05485a40f1b9

• Release notes: https://github.com/protocolbuffers/protobuf/releases/tag/v3.15.0

• Diff: https://github.com/protocolbuffers/protobuf/compare/v3.14.0...v3.15.8

Relates to #330003 (closed)