tests: Listen only on IPv4

Some of the CI runners don't support IPv6, so only listen on IPv4.
5 jobs for fix-16 in 2 minutes and 32 seconds
Status Job ID Name Coverage
  Build
passed #1250304
fedora

00:02:32

51.0%
canceled #1246380
fedora

00:00:17

canceled #1246381
fedora

00:00:02

canceled #1246383
fedora

00:00:15

passed #1246388
fedora

00:03:07

51.1%