[FIX] event_sale: canceled registrations
[FIX] event_sale: canceled registrations

- Open an event registration page
- Fill form for 2 persons => redirection to /shop/checkout
- Click Review Order => open /shop/cart
- Change quantity from 2 to 1
- Finish checkout process
- Login to backend, confirm SO

Two tickets are confirmed instead of one.

opw-783945

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