Support the KDE Gear kf6 branch as well

The problem I'm trying to fix is CI jobs in the PIM kf6 branches not resulting in artifacts that are considered in subsequent builds by modules depending on them.

See e.g. https://invent.kde.org/pim/pimcommon/-/jobs/889024 which uses kldap from the last seed job run rather than a newer CI job run. KMail builds show the same also for kmailtransport (but that doesn't break the build so it went unnoticed initially), so this seems generic.

Not sure this change does what I think it does, this is based on finding mentions of kf5 and expanding them :)