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/notification_spec.rb

@@ -25,8 +25,7 @@ describe Notification do
         read_notification2 = create(:notification, :read)
         unread_notification = create(:notification)
 
-        expect(Notification.read).to include read_notification1
-        expect(Notification.read).to include read_notification2
+        expect(Notification.read).to match_array [read_notification1, read_notification2]
         expect(Notification.read).not_to include unread_notification
       end
     end
@@ -37,8 +36,7 @@ describe Notification do
         unread_notification1 = create(:notification)
         unread_notification2 = create(:notification)
 
-        expect(Notification.unread).to include unread_notification1
-        expect(Notification.unread).to include unread_notification2
+        expect(Notification.unread).to match_array [unread_notification1, unread_notification2]
         expect(Notification.unread).not_to include read_notification
       end
     end