test: fix gleam_httpc_test.ipv6_test

[sobolevn]

  1) gleam_httpc_test.ipv6_test
     #{function => <<"ipv6_test">>,line => 99,
       message => <<"Assertion pattern match failed">>,
       module => <<"gleam_httpc_test">>,
       value =>
           {error,{failed_to_connect,{posix,<<"nxdomain">>},
                                     {posix,<<"enetunreach">>}}},
       gleam_error => let_assert}
     location: gleam_httpc_test.ipv6_test:99
     stacktrace:
       gleam_httpc_test.ipv6_test
     output: 

Finished in 3.240 seconds
9 tests, 1 failures

Example: https://github.com/gleam-lang/httpc/actions/runs/11917211450/job/33211719847

Let's try this approach.

[lpil]

Could you explain the change here please 🙏

[sobolevn]

https://ipv6.google.com gives 404 now, https://ipv6test.google.com works similar.

[lpil]

What's that error you've pasted above? It's not a 404.

How come the test is passing on GitHub actions now? GitHub doesn't have IPv6 support.