optimizing github actions build using cache

When I was poking around the github actions tab, saw the cache side-bar link, and thought I'd check it out. 

Cache Management with GitHub actions - YouTube

When added to this msbuild action, the OpenCV caching brought down the total build time from 5-8 minutes to just 1.5 minutes - the download and untar from cache happens in 25 seconds instead of the download and unzip from github releases which would take 6 minutes or so.

More references:

link to actions/cache: Cache dependencies and build outputs in GitHub Actions 

via

How do I cache steps in GitHub actions? - Stack Overflow

Need to order the named jobs so that the cache comes first - https://github.com/actions/cache#skipping-steps-based-on-cache-hit