上传mp4文件的时候报错

[Because66666]

Describe the bug
场景：使用bot.client.create_asset上传视频.mp4文件的时候报错。
报错内容：Requesting 'POST asset/create' failed with 40000: Width必须是整数。
报错堆栈：Traceback (most recent call last):
File "C:\Users\Administrator\Downloads_***_bots\kook_bot\kook_bot.py", line 207, in h4
file_url = await bot.client.create_asset(path_to_load) # 上传测试文件
File "C:\Users\Administrator\AppData\Local\Programs\Python\Python310\lib\site-packages\khl\client.py", line 126, in create_asset
return (await self.gate.exec_req(api.Asset.create(file=f)))['url']
File "C:\Users\Administrator\AppData\Local\Programs\Python\Python310\lib\site-packages\khl\gateway.py", line 30, in exec_req
return await self.requester.exec_req(r)
File "C:\Users\Administrator\AppData\Local\Programs\Python\Python310\lib\site-packages\khl\requester.py", line 48, in exec_req
return await self.request(r.method, r.route, **r.params)
File "C:\Users\Administrator\AppData\Local\Programs\Python\Python310\lib\site-packages\khl\requester.py", line 39, in request
raise HTTPRequester.APIRequestFailed(method, route, params, rsp['code'], rsp['message'])
khl.requester.HTTPRequester.APIRequestFailed: Requesting 'POST asset/create' failed with 40000: Width必须是整数。

Expected behavior
正常的上传文件

Environment

• Python version:3.10.9
• khl.py version:0.3.17
• OS:windows

报错分析
传递给服务器中的请求的headers中content-type字段缺少boundary字段，原因是khl/requester.py中的第471行为
@req('POST', headers={'Content-Type': 'multipart/form-data'})
指定了content-type。

推荐解决办法
将@req('POST', headers={'Content-Type': 'multipart/form-data'})改为@req('POST')，此时程序会自动指定content-type字段