With 2001:db8::1 allowlisted, Go's URL parser, which the fetcher uses,
reads 2001:db8::1:8443 as 2001:db8::1 with port 8443, and
2001:db8::1: as 2001:db8::1 with an empty port. Both must need a
signature. The test fails until the port check reads the port as the
parsed URL does.
Model: opus-5-5