Only load seed data in development

The CI build calls `db:setup` which was attempting to load a
seeds/test.db file. We don't need to do this in CI, so I've added a
guard.

db/seeds.rb

@@ -1,3 +1,3 @@
 # frozen_string_literal: true
 
-load(Rails.root.join('db', 'seeds', "#{Rails.env.downcase}.rb"))
+load(Rails.root.join('db/seeds/development.rb')) if Rails.env.development?