/usr/include/KF5/akonadi/calendar/ is in libkf5akonadicalendar-dev 4:17.12.3-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/KF5/akonadi/calendar/akonadi-calendar_export.h
/usr/include/KF5/akonadi/calendar/blockalarmsattribute.h
/usr/include/KF5/akonadi/calendar/calendarbase.h
/usr/include/KF5/akonadi/calendar/calendarclipboard.h
/usr/include/KF5/akonadi/calendar/calendarsettings.h
/usr/include/KF5/akonadi/calendar/etmcalendar.h
/usr/include/KF5/akonadi/calendar/fetchjobcalendar.h
/usr/include/KF5/akonadi/calendar/freebusymanager.h
/usr/include/KF5/akonadi/calendar/freebusyproviderbase.h
/usr/include/KF5/akonadi/calendar/history.h
/usr/include/KF5/akonadi/calendar/icalimporter.h
/usr/include/KF5/akonadi/calendar/incidencechanger.h
/usr/include/KF5/akonadi/calendar/itiphandler.h
/usr/include/KF5/akonadi/calendar/publishdialog.h
/usr/include/KF5/akonadi/calendar/standardcalendaractionmanager.h
/usr/include/KF5/akonadi/calendar/todopurger.h