job-runner: timeout task does not cancel if other tasks hang

[jelly]

When podman run --init gets stuck the timeout task does not "kill the job runner" as other tasks might get stuck in gather_and_cancel waiting on task.cancel() to complete:

For example:

await task <Task cancelling name='Task-4' coro=<run_container() running at /home/jelle/projects/cockpit-bots/lib/aio/job.py:125> wait_for=<Future cancelled>>
DEBUG:lib.aio.spawn:run(['podman', 'rm', '--force', '--time=0', '--cidfile=/tmp/tmpw4b91s99/cidfile'])
DEBUG:lib.aio.spawn:run: waiting for pid 64905
Error: reading CIDFile: open /tmp/tmpw4b91s99/cidfile: no such file or directory
DEBUG:lib.aio.spawn:run: pid 64905 exited, 125
DEBUG:lib.aio.spawn:spawn: waiting for pid 64890

Waiting for pid 64890 may take time.

[jelly]

A solution is jelly@21939fc but this races with podman rm....

DEBUG:lib.aio.job:CLEANUP
DEBUG:lib.aio.spawn:run(['podman', 'rm', '--force', '--time=0', '--cidfile=/tmp/tmp9ml5xof8/cidfile'])
DEBUG:lib.aio.spawn:run: waiting for pid 122010
DEBUG:lib.aio.spawn:run: pid 122010 exited, 0
ERROR:lib.aio.job:test timed out
DEBUG:lib.aio.spawn:spawn: waiting for pid 121533
DEBUG:lib.aio.spawn:spawn: pid 121533 exited, 137
DEBUG:lib.aio.github:POST statuses/repos/cockpit-project/cockpit-podman/statuses/4f28caf541312264c31680b6b1ae3e0f59c7aaae error Internal error
DEBUG:lib.aio.local:Write /home/jelle/.cache/cockpit-dev/job-runner-logs/cockpit-project/cockpit-podman/-/4f28caf54131/log
DEBUG:lib.aio.local:Delete /home/jelle/.cache/cockpit-dev/job-runner-logs/cockpit-project/cockpit-podman/-/4f28caf54131/log.0-2451
DEBUG:lib.aio.local:Delete /home/jelle/.cache/cockpit-dev/job-runner-logs/cockpit-project/cockpit-podman/-/4f28caf54131/log.0-446
DEBUG:lib.aio.local:Delete /home/jelle/.cache/cockpit-dev/job-runner-logs/cockpit-project/cockpit-podman/-/4f28caf54131/log.chunks
DEBUG:lib.aio.local:Write /home/jelle/.cache/cockpit-dev/job-runner-logs/cockpit-project/cockpit-podman/-/4f28caf54131/index.html
Traceback (most recent call last):
  File "/usr/lib/python3.13/asyncio/tasks.py", line 507, in wait_for
    return await fut
           ^^^^^^^^^
  File "/home/jelle/projects/cockpit-bots/lib/aio/job.py", line 205, in wait_for_test_completion
    async for block in read_utf8(container.stdout):
    ...<5 lines>...
                sys.stdout.write(block)
  File "/home/jelle/projects/cockpit-bots/lib/aio/util.py", line 127, in read_utf8
    while data := await stream.read(1 << 20):  # 1MB
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.13/asyncio/streams.py", line 730, in read
    await self._wait_for_data('read')
  File "/usr/lib/python3.13/asyncio/streams.py", line 539, in _wait_for_data
    await self._waiter
asyncio.exceptions.CancelledError

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

Traceback (most recent call last):
  File "/home/jelle/projects/cockpit-bots/lib/aio/job.py", line 119, in run_container
    await asyncio.wait_for(wait_for_test_completion(container, attachments, ctx, log, tmpdir),
                           timeout=30)
  File "/usr/lib/python3.13/asyncio/tasks.py", line 506, in wait_for
    async with timeouts.timeout(timeout):
               ~~~~~~~~~~~~~~~~^^^^^^^^^
  File "/usr/lib/python3.13/asyncio/timeouts.py", line 116, in __aexit__
    raise TimeoutError from exc_val
TimeoutError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/jelle/projects/cockpit-bots/./job-runner", line 86, in <module>
    asyncio.run(main())
    ~~~~~~~~~~~^^^^^^^^
  File "/usr/lib/python3.13/asyncio/runners.py", line 195, in run
    return runner.run(main)
           ~~~~~~~~~~^^^^^^
  File "/usr/lib/python3.13/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/usr/lib/python3.13/asyncio/base_events.py", line 719, in run_until_complete
    return future.result()
           ~~~~~~~~~~~~~^^
  File "/home/jelle/projects/cockpit-bots/./job-runner", line 82, in main
    await run_job(job, ctx)
  File "/home/jelle/projects/cockpit-bots/lib/aio/job.py", line 162, in run_job
    await gather_and_cancel(tasks)
  File "/home/jelle/projects/cockpit-bots/lib/aio/util.py", line 117, in gather_and_cancel
    done.result()  # to raise the exception, if applicable
    ~~~~~~~~~~~^^
  File "/home/jelle/projects/cockpit-bots/lib/aio/job.py", line 123, in run_container
    container.kill()
    ~~~~~~~~~~~~~~^^
  File "/usr/lib/python3.13/asyncio/subprocess.py", line 146, in kill
    self._transport.kill()
    ~~~~~~~~~~~~~~~~~~~~^^
  File "/usr/lib/python3.13/asyncio/base_subprocess.py", line 172, in kill
    self.send_signal(signal.SIGKILL)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.13/asyncio/base_subprocess.py", line 162, in send_signal
    self._check_proc()
    ~~~~~~~~~~~~~~~~^^
  File "/usr/lib/python3.13/asyncio/base_subprocess.py", line 146, in _check_proc
    raise ProcessLookupError()
ProcessLookupError