fix: Converting before parameter of list_public_archived_threads() to ISO8601

[kpodp0ra]

What type of pull request is this?

• Non-breaking code change
• Breaking code change
• Documentation change/addition
• Tests change

Description

This PR fixes following error caused by forum.archived_posts() iterator

Traceback (most recent call last):
  File "naff/client/client.py", line 1832, in _dispatch_prefixed_commands
    await self._run_prefixed_command(command, context)
  File "naff/client/client.py", line 1655, in _run_prefixed_command
    return await command(ctx)
  File "naff/models/naff/command.py", line 120, in __call__
    await self.call_callback(self.callback, context)
  File "naff/models/naff/prefixed_commands.py", line 624, in call_callback
    return await self.call_with_binding(callback, ctx)
  File "naff/models/naff/callback.py", line 43, in call_with_binding
    return await callback(*args, **kwargs)
  File "bot/main.py", line 35, in test
    async for post in ch.archived_posts():
  File "naff/models/misc/iterator.py", line 75, in __anext__
    await self._get_items()
  File "naff/models/misc/iterator.py", line 67, in _get_items
    data = await self.fetch()
  File "naff/models/discord/channel.py", line 144, in fetch
    rcv = await self.channel._client.http.list_public_archived_threads(
  File "naff/api/http/http_requests/threads.py", line 96, in list_public_archived_threads
    payload["before"] = timestamp_converter(before)
  File "naff/client/utils/attr_converters.py", line 29, in timestamp_converter
    raise TypeError("Timestamp must be one of: datetime, int, float, ISO8601 str")
TypeError: Timestamp must be one of: datetime, int, float, ISO8601 str

Changes

• Fixed fetching data in forums with more than 100 archived posts.

Checklist

• I've formatted my code with Black
• I've ensured my code works on Python 3.10.x
• I've tested my code

[LordOfPolls]

/ok-to-test