Events with 'When shared show only busy' are ignored by ICalendar>CalendarImpl.php>CalDavBackend.php->search()

Steps to reproduce

1. Share a calendar User1 -> User2
2. User1: create an event with accessClass='When shared show only busy' and timeTransparency='Busy'
   https://github.com/nextcloud/calendar/blob/f39e31fec11708970f975dc83e49246decce95dd/src/models/rfcProps.js#L35-L46
   https://github.com/nextcloud/calendar/blob/f39e31fec11708970f975dc83e49246decce95dd/src/models/rfcProps.js#L82-L92
3. Call ICalendar->search() as User2
   https://github.com/nextcloud/server/blob/eeec6142ca6af64e86d1dde9103fb365a3c5f51d/lib/public/Calendar/ICalendar.php#L61-L71

Expected behavior

User1 set timeTransparency to Busy and accessClass to When shared show only busy therefore the event should be returned when User2 calls the ICalendar->search() function

Actual behaviour

The event is not returned.

CalendarImpl->search() https://github.com/nextcloud/server/blob/5079bf6dd9df1240e88435b56e996b5cd8abde06/apps/dav/lib/CalDAV/CalendarImpl.php#L109-L112
calls CalDavBackend->search() https://github.com/nextcloud/server/blob/532c7545bdc0ba37337d2103a74fce796915539b/apps/dav/lib/CalDAV/CalDavBackend.php#L1826-L1827
and the 'When shared show only busy' (aka CONFIDENTIAL) event is skipped here:
https://github.com/nextcloud/server/blob/532c7545bdc0ba37337d2103a74fce796915539b/apps/dav/lib/CalDAV/CalDavBackend.php#L1837-L1843

*Please that note this bug is specific to ICalendar->serach() because it uses CalDavBackend->search(), while other methods might call CalDavBackend->calendarQuery()

Calendar app version

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CalDAV-clients used

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Browser

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Client operating system

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Server operating system

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Web server

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Database engine version

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PHP engine version

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Nextcloud version

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Updated from an older installed version or fresh install

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List of activated apps

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Nextcloud configuration

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Web server error log

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Log file

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Browser log

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Additional info

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Start with apps/dav/lib/CalDAV/CalendarImpl.php search() and follow its call into CalDavBackend.php search(), especially the access-class filtering around the referenced lines. Compare this path with calendarQuery() and reproduce the shared-calendar case; done means ICalendar->search() returns a Busy event marked “When shared show only busy” for the other user.