qt6 builds: use CURRENT with EXCLUDE_DEPRECATED_BEFORE_AND_AT
This ensures that always the latest KF version is used when deciding what to exclude. Well, at least for what KF version is bumped to, so the week between tag and release, when the version is not yet bumped, that will miss out. Not sure if using simply 6.0.0 would work, might work by chance but needs someone to test (and specify in the macro docs first)