Fix empty line to contain two values

Prior to this change, the empty line between the license information
header and the user count table only contained a single value. This
prevents to convert the license usage file csv into a hash by using to_h
and instead required a manual mapping.
Now, the empty line contains two empty strings to reflect a valid hash
structure.

Changelog: changed
MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/78678
EE: true

ee/app/services/historical_user_data/csv_service.rb

@@ -39,7 +39,7 @@ module HistoricalUserData
         csv << ['License End Date', license.expires_at&.to_s(:csv)]
         csv << ['Company', license.licensee_company]
         csv << ['Generated At', Time.current.to_s(:csv)]
-        csv << ['']
+        csv << ['', '']
       end
     end
   end

ee/spec/services/historical_user_data/csv_service_spec.rb

@@ -92,6 +92,13 @@ RSpec.describe HistoricalUserData::CsvService do
     end
   end
 
+  context 'Empty Row' do
+    it 'adds an empty row between the License Information Header and the User Count Table' do
+      expect(csv[6][0]).to eq('')
+      expect(csv[6][1]).to eq('')
+    end
+  end
+
   context 'User Count Table' do
     let_it_be(:historical_datum) do
       create(:historical_data, recorded_at: license_start_date, active_user_count: 1)