Consider using JSON to get the cmake tarball/zip file

There are some complexity tradeoffs, but using the JOSN would mean not having to parse HTML, or might avoid having to continually update filename patterns.

https://github.com/Kitware/CMake/releases/download/v3.21.0/cmake-3.21.0-files-v1.json

It would be better if the JSON filename wasn't versioned, and there might be other nits that might make it not worth it.