tests: fix ipv6 support in test_push_command.py This test runs the `svnserve` binary, which appears to resolve the hostname passed as an argument using gethostbyname(3), which can only return an IPv4 address. When run on a system that is configured to only have an IPv6 address, Mercurial will correctly resolve the hostname to an IPv6 address, but the SVN server will be listening on an incorrect IPv4 address, causing the test to fail. The workaround is to resolve the hostname using getaddrinfo(3) in the test harness and pass the resulting address to svnserve.