Avoid creating extra poll records in tests

The line:

create(:poll_voter, booth_assignment: booth_assignment_final_recounted)

Creates a new poll for the poll voter. Not only it wastes time by
creating new database records, but it doesn't make sense to have a poll
voter for a poll which isn't the same as its booth assignment's poll.

spec/features/admin/poll/polls_spec.rb

@@ -222,7 +222,9 @@ feature "Admin polls" do
                  total_amount: 21)
         end
 
-        2.times { create(:poll_voter, booth_assignment: booth_assignment_final_recounted) }
+        2.times do
+          create(:poll_voter, poll: poll, booth_assignment: booth_assignment_final_recounted)
+        end
 
         create(:poll_recount,
                booth_assignment: booth_assignment_final_recounted,