D23202: Fix headers for >=KCalCore-5.12.0

[David Faure]

dfaure added a reviewer: vkrause.

REPOSITORY
  R8 Calligra

REVISION DETAIL
  https://phabricator.kde.org/D23202

To: asturmlechner, #calligra:_3.0, dfaure, vkrause
Cc: Calligra-Devel-list, dcaliste, cochise, vandenoever