Nextcloud 32 compatibility changes needed

[JonathanTreffler]

• feat(dav)!: add webhook compatibility for calendar object events nextcloud/server#51082

  The events we rely on to get calendar change notifications have been renamed and are now in a public namespace (which is good, we don't have to listen to technically private events anymore, but I think it is a bit weird to have such generically named public events, that are actually fixed to the default calendar backend and therefore not as generic as the name would suggest)

[JonathanTreffler]

done