Fix flaky test: Labels CSV needs an organiser

The workshop fabricator no longer creates organisers automatically
after the chapter fabricator optimization. This test needs an organiser
to be present for the CSV to contain 'ORGANISER'.

Author: mroderick

spec/features/admin/workshops_spec.rb

@@ -247,6 +247,10 @@
     context 'Labels' do
       it 'returns a CSV with all workshop participants that can be used to generate the labels' do
         workshop = Fabricate(:workshop)
+        # Add an organiser to ensure ORGANISER appears in the CSV
+        organiser = Fabricate(:member)
+        organiser.add_role :organiser, workshop.chapter
+
         visit admin_workshop_path(workshop)
         click_on 'Labels'