As the message states you will want to check the sharp docs about this, you will probably need to compile it from source or request from your system/network/security ops to add an exception to allow connections to GitHub. It’s quite common where an NPM package will request additional information from a repo hosting binaries or in some cases a package can have dependencies not on NPM (GitHub can now also host packages and they are moving towards that)
GitHub/Microsoft now own NPM, you should expect more integration between GitHub and NPM.