docs: guild.owner_id type mismatch between docs and code

[nerd-bear]

Summary

Guild.owner_id documented as int, but is Optional[int] in code. Here are the links:
https://docs.disnake.dev/en/stable/api/guilds.html#disnake.Guild.owner_id
disnake/disnake/guild.py
disnake/disnake/guild.py

Checklist

• If code changes were made, then they have been tested
  • I have updated the documentation to reflect the changes
  • I have formatted the code properly by running pdm lint
  • I have type-checked the code by running pdm pyright
• This PR fixes an issue
• This PR adds something new (e.g. new method or parameters)
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)