The listening TCP socket is closed by `with_udp_and_tcp` helper, but
the connected socket is leaking.

```
Leaked file descriptor: TestResolvDNS#test_multiple_servers_with_timeout_and_truncated_tcp_fallback: 12 : #<TCPSocket:fd 12, AF_INET, 127.0.0.1, 50888>
COMMAND     PID     USER   FD   TYPE    DEVICE SIZE/OFF NODE NAME
ruby    3248055 chkbuild   12u  IPv4 112546322      0t0  TCP localhost:50888->localhost:40112 (CLOSE_WAIT)
```

For the purpose of the test case to simulate a timeout over TCP
transport, we have to delay closing this socket until the end the test
case.

Fixup: https://github.com/ruby/resolv/pull/50

https://github.com/ruby/resolv/commit/236c38bdb1