Improve the testing of `local` to tolarate IPv6 link-local addresses

[favonia]

For some reasons, testing local in some IPv6-enabled network using ::1 (instead of the real Cloudflare server) leads to a link-local address. Not sure if this is intended, but the testing failed because of it. (Note: the tool uses the real Cloudflare server outside the testing, and this strange behavior should never happen.)