Various tests fail due to starting kernel on wrong Python version

With `ipykernel-6.0.1`:

```pytb
$ PYTHONPATH=. python3.8 -m pytest -x ipykernel/tests/test_async.py
========================================================= test session starts =========================================================
platform linux -- Python 3.8.11, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
rootdir: /tmp/ipykernel-6.0.1
plugins: timeout-1.4.2, case-1.5.3, xprocess-0.17.1, mock-3.6.1, localserver-0.5.0, expect-1.1.0, httpx-0.12.0, asyncio-0.15.1, snapshottest-0.5.1, forked-1.3.0, freezegun-0.4.2, datadir-1.3.1, metadata-1.8.0, requests-mock-1.9.3, subtests-0.5.0, betamax-0.8.1, regressions-2.2.0, pyfakefs-4.5.0, httpbin-1.0.0, django-4.4.0, shutil-1.7.0, virtualenv-1.7.0, subtesthack-0.1.2, pkgcore-0.12.1, xdist-2.3.0, pylama-7.7.1, cov-2.12.1, xdoctest-0.15.4, anyio-3.2.1, hypothesis-6.14.1, rerunfailures-10.1, flaky-3.7.0, services-2.2.1, aiohttp-0.3.0, Faker-8.10.0, lazy-fixture-0.6.3, xvfb-2.0.0, trio-0.7.0
collected 4 items

ipykernel/tests/test_async.py E

=============================================================== ERRORS ================================================================
_________________________________________________ ERROR at setup of test_async_await __________________________________________________

def setup_function():
"""start the global kernel (if it isn't running) and return its client"""
global KM, KC
> KM, KC = start_new_kernel()

ipykernel/tests/test_async.py:20:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
ipykernel/tests/utils.py:37: in start_new_kernel
return manager.start_new_kernel(startup_timeout=STARTUP_TIMEOUT, **kwargs)
/usr/lib/python3.8/site-packages/jupyter_client/manager.py:919: in start_new_kernel
kc.wait_for_ready(timeout=startup_timeout)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = , timeout = 60

def wait_for_ready(self, timeout=None):
"""Waits for a response when a client is blocked

- Sets future time for timeout
- Blocks on shell channel until a message is received
- Exit if the kernel has died
- If client times out before receiving a message from the kernel, send RuntimeError
- Flush the IOPub channel
"""
if timeout is None:
abs_timeout = float('inf')
else:
abs_timeout = time.time() + timeout

from ..manager import KernelManager
if not isinstance(self.parent, KernelManager):
# This Client was not created by a KernelManager,
# so wait for kernel to become responsive to heartbeats
# before checking for kernel_info reply
while not self.is_alive():
if time.time() > abs_timeout:
raise RuntimeError("Kernel didn't respond to heartbeats in %d seconds and timed out" % timeout)
time.sleep(0.2)

# Wait for kernel info reply on shell channel
while True:
self.kernel_info()
try:
msg = self.shell_channel.get_msg(block=True, timeout=1)
except Empty:
pass
else:
if msg['msg_type'] == 'kernel_info_reply':
# Checking that IOPub is connected. If it is not connected, start over.
try:
self.iopub_channel.get_msg(block=True, timeout=0.2)
except Empty:
pass
else:
self._handle_kernel_info_reply(msg)
break

if not self.is_alive():
> raise RuntimeError('Kernel died before replying to kernel_info')
E RuntimeError: Kernel died before replying to kernel_info

/usr/lib/python3.8/site-packages/jupyter_client/blocking/client.py:111: RuntimeError
-------------------------------------------------------- Captured stdout setup --------------------------------------------------------
Traceback (most recent call last):
File "/usr/lib/python3.10/runpy.py", line 196, in _run_module_as_main
return _run_code(code, main_globals, None,
File "/usr/lib/python3.10/runpy.py", line 86, in _run_code
exec(code, run_globals)
File "/tmp/ipykernel-6.0.1/ipykernel_launcher.py", line 15, in
from ipykernel import kernelapp as app
File "/tmp/ipykernel-6.0.1/ipykernel/kernelapp.py", line 42, in
from .ipkernel import IPythonKernel
File "/tmp/ipykernel-6.0.1/ipykernel/ipkernel.py", line 20, in
from .debugger import Debugger
File "/tmp/ipykernel-6.0.1/ipykernel/debugger.py", line 14, in
import debugpy
ModuleNotFoundError: No module named 'debugpy'
======================================================= short test summary info =======================================================
ERROR ipykernel/tests/test_async.py::test_async_await - RuntimeError: Kernel died before replying to kernel_info
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! stopping after 1 failures !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
========================================================== 1 error in 2.83s ===========================================================
```

If add some debug, it turns out that the underlying cause is that the kernel is started using `python3.10` rather than `python3.8` (and debugpy doesn't support py3.10). This might be a problem in jupyter_client (version 6.1.12 here) but figuring out where it forces `python3.10` is above my pay grade.

Reproduce the failure with ipykernel/tests/test_async.py and inspect ipykernel/tests/utils.py, especially start_new_kernel. Follow the call into jupyter_client's manager.start_new_kernel and compare it with the Python executable running pytest. Done means the affected tests start the kernel with the intended interpreter and no longer fail from the version mismatch.

Scritto dal modello di indicizzazione a partire dal testo della issue.