Add PHP8.3 support

## Describe the task

https://php.watch/news/2023/08/php83-rc1-released

### Affected components

Calendar, Contacts, Mail

## To do

- [x] https://github.com/nextcloud/mail/issues/8918
- [x] https://github.com/nextcloud/contacts/issues/3641
- [x] https://github.com/nextcloud/calendar/issues/5507

## Additional context

- https://github.com/nextcloud/server/pull/40630
