fix: flaky tests in CI

Fix two flaky tests that were failing intermittently in CI:

1. spec/features/listing_coaches_spec.rb:2
   - Changed to use a workshop with a date in the current year (beginning_of_year + 1.month)
     instead of the default future date to ensure the coach is counted for the current year query
   - Added 5 second wait to the expectation for page load timing

2. spec/features/admin/manage_workshop_attendances_spec.rb:25
   - Added explicit wait for '.cancel_attendance' element to be present
     before attempting to click it
   - This ensures the element is rendered before interaction

These changes make the tests more robust in parallel CI execution where
timing and database state can vary between test runs.

Author: mroderick

spec/features/admin/manage_workshop_attendances_spec.rb

@@ -24,6 +24,7 @@
 
     scenario 'can remove a member from the attendee list' do
       visit admin_workshop_path(workshop)
+      expect(page).to have_css('.cancel_attendance', wait: 5)
       find('.cancel_attendance').click
 
       expect(page).to have_content('0 are attending as students')

spec/features/listing_coaches_spec.rb

@@ -1,8 +1,10 @@
 RSpec.feature 'when visiting the coaches page', type: :feature do
   scenario 'I can see the most active coaches' do
-    coach = Fabricate(:attended_coach).member
+    # Use a past workshop date in the current year to ensure the coach is counted
+    workshop = Fabricate(:workshop, date_and_time: Time.zone.today.beginning_of_year + 1.month)
+    coach = Fabricate(:attended_coach, workshop: workshop).member
     visit coaches_path
-    expect(page).to have_content coach.name
+    expect(page).to have_content(coach.name, wait: 5)
   end
 
   scenario 'I can see the top coaches by year' do