Ticket quantity does not reduce until paid

[haqadn]

Describe the bug
The ticket quantity is not reduced until the payment is complete. This makes it possible to oversell tickets.

To reproduce

Steps to reproduce the behavior:

1. Create a paid ticket with quantity 1.
2. As a visitor, fill out the information for this ticket and go to the payments page.
3. From a different tab, as a visitor again, fill out the information for the ticket and go to the payment page again.
4. Pay for both tickets.
5. You should now have sold two tickets even though only one was available.

Expected behavior

The ticket should have said unavailable as soon as the first form was submitted, and the the second ticket purchase should have stopped in two places:

1. Before accessing the check-out form.
2. After submitting and being redirected to the checkout-form.

Screenshots / Screencasts

None

WordCamp

This was experienced on WordCamp Sylhet 2024 (and 2023). But, it's not specific to any WordCamps.

System (please complete the following information):
N/A