Update all IP Addresses in tests to use RFC-5735 TEST-NET-* addresses.

nitpick: ‏super nitpicky, and not the first violation of this type in the codebase, but per RFC-5735 we ought to use addresses in TEST-NET-* ranges. Thankfully we have pytest-socket (#humbebrag) to prevent actual network calls, so it's not an issue, but I wanted to note it while it was fresh in my head. (Also see https://www.rfc-editor.org/rfc/rfc6890#section-2.2.2) Might be worth a full sweep cleanup as a separate PR.

Originally posted by @miketheman in https://github.com/pypi/warehouse/pull/13164#discussion_r1131763629