jupyter-available-kernelspecs fails with Python 3.11

[dlukes]

jupyter kernelspec list --json emits a warning to stderr, which jupyter-available-kernelspecs fails to separate from stdout, and therefore parsing fails:

0.00s - Debugger warning: It seems that frozen modules are being used, which may
0.00s - make the debugger miss breakpoints. Please pass -Xfrozen_modules=off
0.00s - to python to disable frozen modules.
0.00s - Note: Debugging will proceed. Set PYDEVD_DISABLE_FILE_VALIDATION=1 to disable this validation.
{
  "kernelspecs": { ... }
}

The warning is emitted by pydevd, vendored by debugpy, required by ipykernel.

Workaround: setting the environment variable PYDEVD_DISABLE_FILE_VALIDATION=1 to silence the warning (as suggested by the message). Ignoring the warning should be safe with recent enough versions of debugpy since microsoft/debugpy#937.

Fix: jupyter-command should discard stderr, or possibly output it as a message, instead of combining it with stdout.