Reduce responsibility of UrlBlocker#get_address_info

What does this MR do and why?

In some situations UrlBlocker.validate! considers a URI that we cannot retrieve the addrinfo for to be valid.

This was previously signalled in code when UrlBlocker#get_address_info would return a nil value. The calling code in .validate! would then handle the nil value in a way that treated the URI as valid.

This behaviour was reasonably opaque to the reader of the code.

This change makes this behaviour of .validate! more clear and more explicit.

See: !112771 (comment 1292643144)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.