feat: add source_invite_code to guildmemberdata

[LawMixer]

Drafting this pull request until it is officially added to Discord API, though it is soft released just not announced. Will undraft it when it is timed to merge it.

Link: discord/discord-api-docs#3210 (comment)

[LawMixer]

I'm ready whenever the maintainers are, everything should be completed! Thank you!

[Bluenix2]

Hi, I've been thinking about this pull request a bit, and waiting to hear about any official news.

Thanks a lot for your first PR! ❤️ Do you know more about the nature of this new field than the discussion you linked?

I am hesitant to add unofficial fields because they can quickly grow out of hand, but that isn't to say that this library follows the docs religiously. It deviates from the docs when doing so improves the typing experience (such as in the case of channels). However, I don't believe this field matches that criteria.

Because it isn't in the official docs, and a quick search on discord-api-types didn't give any results (as of writing), I would like to hold off on merging this unless there is a big need to.

Thanks again!

[LawMixer]

This change has been slowly coming out for all users, though it seems Discord has not made any pull request for their API documentations for this. Thank you for having me! <3

I just committed a new version with your changes, let me know if there's anything else I can do!

[LawMixer]

Thanks a lot for your first PR! ❤️ Do you know more about the nature of this new field than the discussion you linked?

No yet announced from Discord officially, but we've seen ``source_invite_code show up in the Members page on people's discord server, and it is in the member search endpoint.

We've gotten an update from Discord Support on X that pushed things along wayyy quicker, so if you want to wait on them for the official announcement of this change, that's fine by me.