Move admin creation into shared let on spec

spec/features/tags/budget_investments_spec.rb

@@ -8,6 +8,7 @@ feature 'Tags' do
   let!(:heading) { create(:budget_heading, name: "More hospitals", group: group) }
   let!(:tag_medio_ambiente) { create(:tag, :category, name: 'Medio Ambiente') }
   let!(:tag_economia) { create(:tag, :category, name: 'Economía') }
+  let(:admin) { create(:administrator).user }
 
   scenario 'Index' do
     earth = create(:budget_investment, heading: heading, tag_list: tag_medio_ambiente.name)
@@ -282,8 +283,7 @@ feature 'Tags' do
       investment.set_tag_list_on(:valuation, 'Education')
       investment.save
 
-      admin = create(:administrator)
-      login_as(admin.user)
+      login_as(admin)
 
       visit admin_budget_budget_investment_path(budget, investment)
       click_link 'Edit classification'