Promote json-schema to production

This was introduced in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/32991 and used in
app/validators/json_schema_validator.rb, so we need it as a production
gem instead of a test gem.

This caused
https://gitlab.com/gitlab-com/gl-infra/production/-/issues/2207

Gemfile

@@ -402,7 +402,6 @@ group :test do
 
   gem 'shoulda-matchers', '~> 4.0.1', require: false
   gem 'email_spec', '~> 2.2.0'
-  gem 'json-schema', '~> 2.8.0'
   gem 'webmock', '~> 3.5.1'
   gem 'rails-controller-testing'
   gem 'concurrent-ruby', '~> 1.1'
@@ -497,3 +496,4 @@ gem 'valid_email', '~> 0.1'
 
 # JSON
 gem 'json', '~> 2.3.0'
+gem 'json-schema', '~> 2.8.0'

app/validators/json_schema_validator.rb

 # frozen_string_literal: true
-
-require "json-schema"
-
+#
 # JsonSchemaValidator
 #
 # Custom validator for json schema.