Ensure the cache content is minimum required

[lukka]

As reported in #171 (comment), excluded directories, like vcpkg/buildtrees, are being stored in the cloud based GH cache used by run-vcpkg.
This behavior is a bug in the cache API that is not addressed, e.g.:

• Glob patterns should work for excludes actions/cache#364
• Cache - excluding files or folders with ! not working actions/toolkit#713

A workaround should be applied to run-vcpkg to avoid saving into the cache unnecessary content.