chore(test): make proxy test robust wrt IPv4/v6

[Fabian-Gruenbichler]

this test fails if hyper.rs resolves to an IPv6 address in the test env otherwise:

running 1 test

thread 'test_socks_v5_with_locally_resolved_domain_works' panicked at tests/proxy.rs:331:9:
assertion `left == right` failed
  left: [5, 1, 0, 4]
 right: [5, 1, 0, 1]
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

thread 'test_socks_v5_with_locally_resolved_domain_works' panicked at tests/proxy.rs:301:14:
tunnel: Io(Custom { kind: UnexpectedEof, error: "unexpected eof" })

thread 'test_socks_v5_with_locally_resolved_domain_works' panicked at tests/proxy.rs:338:14:
task - client: JoinError::Panic(Id(1), "tunnel: Io(Custom { kind: UnexpectedEof, error: \"unexpected eof\" })", ...)
test test_socks_v5_with_locally_resolved_domain_works ... FAILED

failures:

failures:
    test_socks_v5_with_locally_resolved_domain_works

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 6 filtered out; finished in 0.01s

the full message returned by the test proxy:

[5, 1, 0, 4, 38, 6, 71, 0, 48, 55, 0, 0, 0, 0, 0, 0, 104, 21, 12, 232, 1, 187,0, ..] where [4..] of that in hex is ['0x26', '0x6', '0x47', '0x0', '0x30', '0x37', '0x0', '0x0', '0x0', '0x0', '0x0', '0x0', '0x68', '0x15', '0xc', '0xe8', '0x1', '0xbb'] which corresponds to

$ host hyper.rs
...
hyper.rs has IPv6 address 2606:4700:3037::6815:ce8
...

[seanmonstar]

Thanks!