Latest version of aiohttp:
When making connection to a Websocket, the header argument is ignored.

The consequence is that you cannot make a connection to most online MQTT broker's over websocket
because they need the header entry: "Sec-WebSocket-Protocol":"mqtt" in the handshake of
the upgrade protocol.

See this small example code:
It connects to a MQTT broker and then sends the CONNECT mqtt packet.
Then it should get a reply of opcode:2, data: b' \x02\x00\x00' where 'data' is a CONNACK mqtt package
Because of the missing header entry "Sec-WebSocket-Protocol":"mqtt" most brokers will refuse the connection or
refuse to accept MQTT packets.

import aiohttp
import asyncio

async def connect():
    url = "ws://test.mosquitto.org:8080"
    headers = {"Sec-WebSocket-Protocol":"mqtt"}
    connect_pkt = bytearray(b'\x10\x10\x00\x04MQTT\x04\x02\x00x\x00\x04fz54')
    
    async with aiohttp.ClientSession(headers=headers).ws_connect(url) as ws:
            print("Connected")
            await ws.send_bytes(connect_pkt)
            opcode, data = await ws.ws.receive()
            print(f"opcode:{opcode}, data{data}")

asyncio.run(connect())