Event attachment: Attachments are not shared with calender recipients

[susnux]

Steps to reproduce

1. Create a calendar
2. Share calendar with other user or groups
3. Create new event and attach a file
4. See that other people with access to the calendar (through group or user share) have no access to the attachment

Expected behavior

Shared calendars should automatically share all attachments with all sharees.

Actual behavior

File are only accessible by attendees or creator of the attachment, but not other calendar recipients,

Calendar app version

6.1.5

Nextcloud version

Nextcloud 32 and 31 tested.

Additional info

Probably it makes sense to upload attachments into shared folders with the same shares as the calendar itself has.
This way all attached files are accessible to other user of the same calendar.