Used seed-fu in db/fixtures/test/01_plan.rb so that if seed-fu is broken, we'll catch it

Signed-off-by: Rémy Coutable <remy@rymai.me>

db/fixtures/test/01_admin.rb

-require './spec/support/sidekiq'
-
-Gitlab::Seeder.quiet do
-  User.seed do |s|
-    s.id = 1
-    s.name = 'Administrator'
-    s.email = 'admin@example.com'
-    s.notification_email = 'admin@example.com'
-    s.username = 'root'
-    s.password = '5iveL!fe'
-    s.admin = true
-    s.projects_limit = 100
-    s.confirmed_at = DateTime.now
-  end
-end

db/fixtures/test/01_plan.rb

 require './spec/support/sidekiq'
 
-Plan.create!(name: EE::Namespace::FREE_PLAN,
+Plan.seed(name: EE::Namespace::FREE_PLAN,
              title: EE::Namespace::FREE_PLAN.titleize)
 
 EE::Namespace::NAMESPACE_PLANS_TO_LICENSE_PLANS.each_key do |plan|
-  Plan.create!(name: plan, title: plan.titleize)
+  Plan.seed(name: plan, title: plan.titleize)
 end