Disable broken RKWard_Release_MinGW build

I am not sure this is the correct approach at all, but trying to fix this failure: https://binary-factory.kde.org/view/Windows%20MingW/job/RKWard_Release_mingw64/lastFailedBuild/consoleFull

Update: All different approach to the same problem, now, but keeping it in this merge request to keep discussion in one place.