t/local/referer.t blocking forever during autopkgtests

The test file t/local/referer.t will block forever on Ubuntu's autopkgtest runners.

There is a similar problem reported upstream a few years ago but I'm not sure they are related. I added more details to it https://github.com/libwww-perl/WWW-Mechanize/issues/281

referer.t will start a local webserver implemented in t/local/referer-server. Each test will call the webserver and stop it by calling GET /quit-server in the last test. Although, in the end, referer.t blocks on wait(referer-server), supposedly after calling close(), but referer-server is blocked on accept().

These tests will just work locally and are not blocking on Debian.