Runners don't support IPv6
For example, pipeline https://gitlab.freedesktop.org/pwithnall/uhttpmock/-/pipelines/631823 failed with:
Bail out! libuhttpmock:ERROR:../libuhttpmock/uhm-server.c:1398:uhm_server_run: assertion failed (error == NULL): Could not listen on address ::1, port 39835: Error binding to address [::1]:39835: Cannot assign requested address (g-io-error-quark, 0)
Edited by Daniel Stone