Bump pg from 1.5.4 to 1.5.6

Bumps [pg](https://github.com/ged/ruby-pg) from 1.5.4 to 1.5.6.
- [Changelog](https://github.com/ged/ruby-pg/blob/master/History.md)
- [Commits](https://github.com/ged/ruby-pg/compare/v1.5.4...v1.5.6)

---
updated-dependencies:
- dependency-name: pg
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Gemfile

@@ -34,7 +34,7 @@ gem 'mini_racer', group: :therubyracer
 # Use --without <group> argument to skip unnecessary drivers
 gem 'sqlite3', group: :sqlite
 gem 'mysql2', '~> 0.5.6', group: :mysql
-gem 'pg', '~> 1.5.4', group: :postgresql
+gem 'pg', '~> 1.5.6', group: :postgresql
 
 group :development do
   gem 'spring', '~> 4'

Gemfile.lock

@@ -200,7 +200,7 @@ GEM
     parser (3.2.2.4)
       ast (~> 2.4.1)
       racc
-    pg (1.5.4)
+    pg (1.5.6)
     puma (6.4.2)
       nio4r (~> 2.0)
     racc (1.8.0)
@@ -377,7 +377,7 @@ DEPENDENCIES
   minitest-stub-const
   mocha
   mysql2 (~> 0.5.6)
-  pg (~> 1.5.4)
+  pg (~> 1.5.6)
   puma (~> 6.4)
   rack-mini-profiler
   rails (~> 6.1)