Update pg gem to v1.2.2

This adds support for Ruby 2.7 and PostgreSQL 12. Omnibus is also
shipping two versions of the pg gem (v1.2.2 and v1.1.4), so let's make
this consistent.

Full list of changes:
https://github.com/ged/ruby-pg/blob/master/History.rdoc

Gemfile.lock

@@ -741,7 +741,7 @@ GEM
     parslet (1.8.2)
     peek (1.1.0)
       railties (>= 4.0.0)
-    pg (1.1.4)
+    pg (1.2.2)
     png_quantizator (0.2.1)
     po_to_json (1.0.1)
       json (>= 1.6.0)

changelogs/unreleased/sh-bump-pg-gem-1-2-2.yml

+---
+title: Update pg gem to v1.2.2
+merge_request: 23237
+author:
+type: other