Check exact array contents instead of inclusion

We're using `eq` and `match_array` in most places, but there were a few
places where we were still checking each element is included in the
array. This is a bit dangerous, because the array could have duplicate
elements, and we wouldn't detect them with `include`.

spec/models/poll/booth_spec.rb

@@ -30,7 +30,7 @@ describe Poll::Booth do
       booth_for_current_poll = create(:poll_booth, polls: [create(:poll, :current)])
       booth_for_expired_poll = create(:poll_booth, polls: [create(:poll, :expired)])
 
-      expect(Poll::Booth.available).to include(booth_for_current_poll)
+      expect(Poll::Booth.available).to eq [booth_for_current_poll]
       expect(Poll::Booth.available).not_to include(booth_for_expired_poll)
     end