/usr/share/php/Sabre/CalDAV/ is in php-sabre-dav 1.8.12-1ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/php/Sabre/CalDAV/Backend/
/usr/share/php/Sabre/CalDAV/Backend/AbstractBackend.php
/usr/share/php/Sabre/CalDAV/Backend/BackendInterface.php
/usr/share/php/Sabre/CalDAV/Backend/NotificationSupport.php
/usr/share/php/Sabre/CalDAV/Backend/PDO.php
/usr/share/php/Sabre/CalDAV/Backend/SharingSupport.php
/usr/share/php/Sabre/CalDAV/Calendar.php
/usr/share/php/Sabre/CalDAV/CalendarObject.php
/usr/share/php/Sabre/CalDAV/CalendarQueryParser.php
/usr/share/php/Sabre/CalDAV/CalendarQueryValidator.php
/usr/share/php/Sabre/CalDAV/CalendarRootNode.php
/usr/share/php/Sabre/CalDAV/Exception/
/usr/share/php/Sabre/CalDAV/Exception/InvalidComponentType.php
/usr/share/php/Sabre/CalDAV/ICSExportPlugin.php
/usr/share/php/Sabre/CalDAV/ICalendar.php
/usr/share/php/Sabre/CalDAV/ICalendarObject.php
/usr/share/php/Sabre/CalDAV/IShareableCalendar.php
/usr/share/php/Sabre/CalDAV/ISharedCalendar.php
/usr/share/php/Sabre/CalDAV/Notifications/
/usr/share/php/Sabre/CalDAV/Notifications/Collection.php
/usr/share/php/Sabre/CalDAV/Notifications/ICollection.php
/usr/share/php/Sabre/CalDAV/Notifications/INode.php
/usr/share/php/Sabre/CalDAV/Notifications/INotificationType.php
/usr/share/php/Sabre/CalDAV/Notifications/Node.php
/usr/share/php/Sabre/CalDAV/Notifications/Notification/
/usr/share/php/Sabre/CalDAV/Notifications/Notification/Invite.php
/usr/share/php/Sabre/CalDAV/Notifications/Notification/InviteReply.php
/usr/share/php/Sabre/CalDAV/Notifications/Notification/SystemStatus.php
/usr/share/php/Sabre/CalDAV/Plugin.php
/usr/share/php/Sabre/CalDAV/Principal/
/usr/share/php/Sabre/CalDAV/Principal/Collection.php
/usr/share/php/Sabre/CalDAV/Principal/IProxyRead.php
/usr/share/php/Sabre/CalDAV/Principal/IProxyWrite.php
/usr/share/php/Sabre/CalDAV/Principal/ProxyRead.php
/usr/share/php/Sabre/CalDAV/Principal/ProxyWrite.php
/usr/share/php/Sabre/CalDAV/Principal/User.php
/usr/share/php/Sabre/CalDAV/Property/
/usr/share/php/Sabre/CalDAV/Property/AllowedSharingModes.php
/usr/share/php/Sabre/CalDAV/Property/Invite.php
/usr/share/php/Sabre/CalDAV/Property/ScheduleCalendarTransp.php
/usr/share/php/Sabre/CalDAV/Property/SupportedCalendarComponentSet.php
/usr/share/php/Sabre/CalDAV/Property/SupportedCalendarData.php
/usr/share/php/Sabre/CalDAV/Property/SupportedCollationSet.php
/usr/share/php/Sabre/CalDAV/Schedule/
/usr/share/php/Sabre/CalDAV/Schedule/IMip.php
/usr/share/php/Sabre/CalDAV/Schedule/IOutbox.php
/usr/share/php/Sabre/CalDAV/Schedule/Outbox.php
/usr/share/php/Sabre/CalDAV/ShareableCalendar.php
/usr/share/php/Sabre/CalDAV/SharedCalendar.php
/usr/share/php/Sabre/CalDAV/SharingPlugin.php
/usr/share/php/Sabre/CalDAV/UserCalendars.php
/usr/share/php/Sabre/CalDAV/Version.php