Fix flaky TCPSocket#local_address implicit-hostname spec

The "using an implicit hostname" example connects with TCPSocket.new(nil,
port) to a server bound to the IPv4 loopback, then asserts that
local_address.ip_address equals @host ("127.0.0.1"). This is flaky.

A nil hostname resolves to the loopback of both families, and Happy Eyeballs
prefers IPv6, so the connection is not guaranteed to reach the IPv4 test
server. IPv4 and IPv6 can share the same ephemeral port number (v6only), so
under parallel runs (-j20) an unrelated listener on ::1:<same port> can be
reached instead. local_address then comes back as "::1" and the spec fails.

The invariant the example actually wants to check is that local_address
reflects the connection's family, which always matches the peer. Compare
against remote_address.ip_address instead of @host: deterministic in a clean
environment and robust to the cross-family ephemeral-port collision.

Verified: the spec passes normally, and with a forced ::1 listener on the
same port the old `== @host` assertion fails while `== remote` holds.

(Imported from ruby/spec; should be upstreamed there.)

Error:
  TCPSocket#local_address using IPv4 using an implicit hostname the returned
  Addrinfo uses the correct IP address FAILED
  Expected "::1" == "127.0.0.1" to be truthy but was false
  spec/ruby/library/socket/tcpsocket/local_address_spec.rb:68

CI: https://ci.rvm.jp/results/trunk@ruby-sp3/6380323
Log: https://ci.rvm.jp/logfiles/brlog.trunk.20260616-071309

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 2 people

library/socket/tcpsocket/local_address_spec.rb

@@ -65,7 +65,13 @@
 
       describe 'the returned Addrinfo' do
         it 'uses the correct IP address' do
-          @sock.local_address.ip_address.should == @host
+          # An implicit (nil) hostname resolves to the loopback of either family
+          # and Happy Eyeballs prefers IPv6, so the connection is not guaranteed
+          # to land on @host: under parallel runs an unrelated listener on
+          # ::1:<same ephemeral port> can be reached instead, making @host a
+          # flaky expectation (local_address would be ::1). The local end always
+          # matches the family actually connected, so compare against the peer.
+          @sock.local_address.ip_address.should == @sock.remote_address.ip_address
         end
       end
     end