Bump pg from 1.1.4 to 1.2.3 in /backend

Bumps [pg](https://github.com/ged/ruby-pg) from 1.1.4 to 1.2.3.
- [Release notes](https://github.com/ged/ruby-pg/releases)
- [Changelog](https://github.com/ged/ruby-pg/blob/master/History.rdoc)
- [Commits](ged/ruby-pg@v1.1.4...v1.2.3)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

backend/Gemfile.lock

@@ -102,7 +102,7 @@ GEM
     nio4r (2.5.2)
     nokogiri (1.10.9)
       mini_portile2 (~> 2.4.0)
-    pg (1.1.4)
+    pg (1.2.3)
     public_suffix (4.0.1)
     puma (4.3.5)
       nio4r (~> 2.0)