The test code doesn't mind if you turn the class into a namespace:

namespace ScalingSqStrings
{
    std::string scale(const std::string &strng, int k, int n);
}

Guess the closest you can get to downvote is to mark the kata as none for the How satisfied are you with this kata and its quality? section after completing it.

Yes I understand your point and in later kata I changed that. 200 guys passed the C++ kata and if I change this one it would invalidate their solutions.