Add a regression test for non-inlined dnslinks on localhost tests

Extracting this issue out of https://github.com/ipfs/gateway-conformance/issues/8/

At the moment, we configure Kubo's gateway with inlining on both localhost and subdomains gateways:
https://github.com/ipfs/gateway-conformance/blob/8ee866ca235a0c05690c3de26748bb79a81009cb/kubo-config.example.sh#L13

This test might mean running the conformance test suite twice, once against an inlining gateway and once (with different specs) against a gateway running a different configuration.

- [ ] Is this test still relevant?
- [ ] Can we work around having to run the gateway twice?
- [ ] worst case scenario
- [ ] create a new spec for inlining
- [ ] create a new test suite without inlining (the [current test](https://github.com/ipfs/gateway-conformance/blob/8ee866ca235a0c05690c3de26748bb79a81009cb/tests/subdomain_gateway_ipns_test.go#L17) should be a good starting point)

Start by reviewing tests/subdomain_gateway_ipns_test.go and the referenced Kubo gateway configuration to understand the current inlining setup. Determine whether a non-inlined localhost regression test remains relevant and whether it requires a second gateway configuration or suite. Done means covering non-inlined dnslinks on localhost with a clear, passing conformance test.

Written by the indexing model from the issue text.