Bug report

Bug description:

Seems os.posix_spawn uses new-style argument parsing with kwtuple in a vectorcall function, which can trigger a SystemError instead of a TypeError for invalid keyword-only argument.

Tested on Ubuntu 22.04:

>>> import os
>>> os.posix_spawn("/bin/echo", ["echo", "hi"], os.environ, scheduler=None)
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    os.posix_spawn("/bin/echo", ["echo", "hi"], os.environ, scheduler=None)
    ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
SystemError: new style getargs format but argument is not a tuple

CPython versions tested on:

CPython main branch, 3.9

Operating systems tested on:

Linux

Linked PRs

gh-143698: correctly check scheduler and setpgroup values for os.posix_spawn[p] #143699
[3.14] gh-143698: correctly check scheduler and setpgroup values for os.posix_spawn[p] (GH-143699) #145073
[3.13] gh-143698: correctly check scheduler and setpgroup values for os.posix_spawn[p] (GH-143699) #145074