ctx.channel.purge does not behave as expected in threads with version b7

[challos]

Summary

ctx.channel.purge does not work as expected in threads with version b7

Reproduction Steps

Install pycord b7 (also ensure Discord is uninstalled):
pip install -U py-cord==2.0.0b7

Run the minimum code with a given token, debug guild, etc...

Create a new thread under some text channel in one of the debug guilds. Type a few random messages in this new thread. Run /purging_thread with the test_bot. There should be an error seen in actual results

Minimal Reproducible Code

#!/usr/bin/env python3
import discord
from discord.ext import commands

class DeleteCog(commands.Cog):
    def __init__(self, bot: commands.bot):
        self.bot = bot

    @commands.slash_command(
        name="purging_thread",
        description="Deletes all messages from this bot in a thread.",
    )
    async def purging_thread(self, ctx):
        await ctx.channel.purge(limit=5)


if __name__ == "__main__":

    guilds = [...]
    token = "..."

    bot = discord.Bot(debug_guilds=guilds)
    bot.add_cog(DeleteCog(bot))

    bot.run(token)

Expected Results

Messages in the thread to be deleted.

Actual Results

Ignoring exception in command purging_thread:
Traceback (most recent call last):
File "/home/user/.pyenv/versions/bot_dev/lib/python3.9/site-packages/discord/commands/core.py", line 122, in wrapped
ret = await coro(arg)
File "/home/user/.pyenv/versions/bot_dev/lib/python3.9/site-packages/discord/commands/core.py", line 825, in _invoke
await self.callback(self.cog, ctx, **kwargs)
File "/home/user/git/discord_ui_testing/./testing.py", line 18, in purging_thread
await ctx.channel.purge(limit=5)
File "/home/user/.pyenv/versions/bot_dev/lib/python3.9/site-packages/discord/threads.py", line 475, in purge
return await _purge_messages_helper(
File "/home/user/.pyenv/versions/bot_dev/lib/python3.9/site-packages/discord/abc.py", line 169, in _purge_messages_helper
await strategy(to_delete, reason=reason)
TypeError: delete_messages() got an unexpected keyword argument 'reason'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "/home/user/.pyenv/versions/bot_dev/lib/python3.9/site-packages/discord/bot.py", line 1098, in invoke_application_command
await ctx.command.invoke(ctx)
File "/home/user/.pyenv/versions/bot_dev/lib/python3.9/site-packages/discord/commands/core.py", line 331, in invoke
await injected(ctx)
File "/home/user/.pyenv/versions/bot_dev/lib/python3.9/site-packages/discord/commands/core.py", line 128, in wrapped
raise ApplicationCommandInvokeError(exc) from exc
discord.errors.ApplicationCommandInvokeError: Application Command raised an exception: TypeError: delete_messages() got an unexpected keyword argument 'reason'

Intents

All

System Information

• Python v3.9.5-final
• py-cord v2.0.0-beta
  • py-cord pkg_resources: v2.0.0b7
• aiohttp v3.8.1
• system info: Linux 5.4.0-91-generic AttributeError: discord.client.Client().application_flags #102-Ubuntu SMP Fri Nov 5 16:31:28 UTC 2021

Checklist

• I have searched the open issues for duplicates.
• I have shown the entire traceback, if possible.
• I have removed my token from display, if visible.

Additional Context

One of the helpers on Discord mentioned that if you go to venv/lib/python3.9/site-packages/discord/threads.py, and change line 354 to
async def delete_messages(self, messages: Iterable[Snowflake], *, reason: Optional[str] = None) -> None:
It might fix the issue. I tested their fix and it does fix it.