Make sure our domain to IP resolution supports multiple possible IP ranges in checks

[mrchrisadams]

As detailed in PR #575, we updated the code we use for checking IP ranges to support ipv4 and ipv6 addresses by using a different socket method, socket.getaddrinfo when looking up a domain.

https://github.com/thegreenwebfoundation/admin-portal/pull/575/files

What we probably should do when a domain is looked up is check every possible ip address we get back from socket.getaddrinfo, and only return a green result if they all match.

This is here for us to revisit in future, so we don't forget.