Fix docker exec types

[kasium]

The return types of docker exec_start are always bytes to my experiments

from __future__ import annotations

from docker import APIClient

client = APIClient()

container_id = client.create_container("python:3.12", command="sleep 10")
client.start(container_id)

try:
    exec_id = client.exec_create(container_id, "echo hello")
    res = client.exec_start(exec_id)
    print(type(res))

    exec_id = client.exec_create(container_id, "echo hello")
    res = client.exec_start(exec_id, stream=True)
    print(type(next(res)))

    exec_id = client.exec_create(container_id, "echo hello")
    res = client.exec_start(exec_id, socket=True)
    print(type(next(res)))

    exec_id = client.exec_create(container_id, "echo hello")
    res = client.exec_start(exec_id, demux=True)
    print(type(res[0]))

    exec_id = client.exec_create(container_id, "echo hello")
    res = client.exec_start(exec_id, demux=True, stream=True)
    print(type(next(res)[0]))
finally:
    client.stop(container_id)

Output:

<class 'bytes'>
<class 'bytes'>
<class 'bytes'>
<class 'bytes'>
<class 'bytes'>

[kasium]

Let me have a look on the failed runs

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉