Fix punycode deprecation warning since Node 21

[ehmicky]

The following warning is currently printed when using Node 21:

(node:17753) [DEP0040] DeprecationWarning: The `punycode` module is deprecated. Please use a userland alternative instead.

This is coming from https://github.com/jsdom/whatwg-url/blob/d34854a7af6ed1204f55d7da7761497bad350a7b/src/url-state-machine.js#L2 which is installed through:

└─┬ release-it@16.2.1
  └─┬ @octokit/rest@19.0.13
    └─┬ @octokit/core@4.2.4
      └─┬ @octokit/request@6.2.8
        └─┬ node-fetch@2.6.12
          └── whatwg-url@5.0.0

The latest version of whatwg-url does not print this warning anymore. However, this requires upgrading @octokit/rest from v19 to v20. Doing so would drop support for Node 16 (which is not officially supported anymore by Node.js).

This would also remove the agent feature, which is currently used by the github.proxy option.

release-it/lib/plugin/github/GitHub.js

Lines 181 to 183 in 9e99e2b

	if (proxy) {
	options.request.agent = new ProxyAgent(proxy);
	}

The original PR that removed that feature is octokit/request.js#599. Instead, a custom fetch should be passed instead. If support for Node <18.13.0 is removed, the global fetch() method can be used without printing an experimental warning. Under the hood, it uses undici.fetch(). An Agent can be passed, but I am unclear whether it must be an undici Agent (which would require adding undici as a dependency) or a core Node.js http Agent.

[webpro]

Thanks for the detailed breakdown @ehmicky, I'll look into it.

[webpro]

This should've been fixed by ebc2754 and releasing v17.