hardcode plasma_version_major to 6 for now
as PLASMA_VERSION_MAJOR is still 5, we need it 6 as soon is tagged it can switch back to PLASMA_VERSION_MAJOR
as PLASMA_VERSION_MAJOR is still 5, we need it 6 as soon is tagged it can switch back to PLASMA_VERSION_MAJOR
mentioned in merge request plasma-workspace!3569 (merged)