fix: sending polls with PartialWebhook

[tyrantlink]

Summary

When attempting to send a poll through a PartialWebook with wait set to True, an AttributeError is raised. Full example code below

from discord import Client, Intents, Message, Webhook
from discord.abc import GuildChannel
from aiohttp import ClientSession


BOT_TOKEN = 'token'


client = Client(
    intents=Intents.default() | Intents.message_content
)


@client.event
async def on_message(message: Message) -> None:
    if message.author.bot or message.poll is None:
        return

    assert isinstance(message.channel, GuildChannel)

    full_webhook = await message.channel.create_webhook(name='webhook state bug demo')

    async with ClientSession() as session:
        webhook = Webhook.from_url(
            url=full_webhook.url,
            session=session
        )

        await webhook.send(
            poll=message.poll,
            wait=True
        )

    await full_webhook.delete(reason='webhook state bug demo')


if __name__ == '__main__':
    client.run(BOT_TOKEN)

Information

• 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, typehinting,
  examples, ...).

Checklist

• I have searched the open pull requests for duplicates.
• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why.
• I have updated the changelog to include these changes.

[tyrantlink]

I don't think the state parameter is artificial comment is necessary, but I left it to match the other methods

[Lulalaby]

LGTM