Deps: Update ruby from 3.1.4 to 3.1.6 (#452)

Required to run in Devcontainer.
3.1.4 is a patch version, no longer exists on Microsoft devcontainer Ruby registry.
3.1.6 is the latest stable version of 3.1.

Author: kyleecodes

.ruby-version

@@ -1 +1 @@
-3.1.4
+3.1.6

Gemfile

@@ -3,7 +3,7 @@
 source 'https://rubygems.org'
 git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 
-ruby '3.1.4'
+ruby '3.1.6'
 
 gem 'rails', '~> 7.0', '>= 7.0.8'
 gem 'pg', '~> 1.5', '>= 1.5.3'