Update to KF5 5.76 (which is the last version supporting Qt 5.12). jsc#SLE-13845

- Update to 5.76.0
* New feature release
* For more details please see:
* https://kde.org/announcements/kde-frameworks-5.76.0
- No code change since 5.75.0

- Update to 5.75.0
* New feature release
* For more details please see:
* https://kde.org/announcements/kde-frameworks-5.75.0
- No code change since 5.74.0

- Update to 5.74.0
* New feature release
* For more details please see:
* https://kde.org/announcements/kde-frameworks-5.74.0
- Changes since 5.73.0:
* Clean unused includes
* Use Q_DECLARE_OPERATORS_FOR_FLAGS in same namespace as flags definition
* metainfo.yaml: Add tier key and tweak description
* Remove obsolete COPYING files

- Update to 5.73.0
* New feature release
* For more details please see:
* https://kde.org/announcements/kde-frameworks-5.73.0
- Changes since 5.72.0:
* Use KF-standardized Qt logging categories
* inqlude expects an "## Introduction" section