Add a fixture file that uses seed-fu in the test env so that a borken seed-fu is detected

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