Fix: Issue #351 default server host compatibility with IPv6

[Barnabas]

Closes #351 by un-defining the default server host name and adds a new test which passes on dual-stack machines.

Sadly, this may not be testable on GitHub due to actions/virtual-environments#668.

[v1rtl]

CI seems to fail

probably worth skipping IPv6 tests?

[aarontravass]

any update on this PR?

[v1rtl]

@aarontravass I think GitHub actions don't support IPv6 so I guess I'll just manually remove the failing test and will merge this

[aarontravass]

@aarontravass I think GitHub actions don't support IPv6 so I guess I'll just manually remove the failing test and will merge this

How about testing ipv6 only if run on non github ci/cd runners? Actions has some default variables that you can utilize - https://docs.github.com/en/actions/learn-github-actions/variables#default-environment-variables

For example

const isGithubAction = Boolean(process.env.GITHUB_ACTION)
const agent = new Agent({ family: isGithubAction ? 4 : 6 })

[v1rtl]

@aarontravass good idea, feel free to extend this PR and update the tests