Render header on sdg index page

We no longer show the static header when we have created a
custom header.

app/controllers/sdg/goals_controller.rb

@@ -6,6 +6,7 @@ class SDG::GoalsController < ApplicationController
   def index
     @goals = @goals.order(:code)
     @phases = SDG::Phase.accessible_by(current_ability).order(:kind)
+    @header = WebSection.find_by!(name: "sdg").header
   end
 
   def show