pytest ignores `-P` (avoid prepend) argument provided to Python

Python 3.11, Windows 11, pytest==8.2.2

1. Create new_test.py in your current folder.

import sys
print(sys.path)

2. Run py -P -m pytest new_test.py --capture=no

C:\numpy> py -P -m pytest new_test.py --capture=no
=============================================================================================================== test session starts ===============================================================================================================
platform win32 -- Python 3.11.7, pytest-8.2.2, pluggy-1.5.0
rootdir: C:\\numpy
configfile: pytest.ini
collecting ... ['C:\numpy', 'C:\numpy\\build-install\\usr\\Lib\\site-packages', 'Python311\\python311.zip', 'Python311\\DLLs', 'Python311\\Lib', 'Python311', 'Python311\\Lib\\site-packages', 'Python311\\Lib\\site-packages\\win32', 'Python311\\Lib\\site-packages\\win32\\lib', 'Python311\\Lib\\site-packages\\Pythonwin']
collected 0 items

3. As you can notice C:\numpy is present in sys.path now, therefore import numpy will import numpy not from C:\numpy\\build-install\\usr\\Lib\\site-packages as it's set by PYTHONPATH environment variable but from C:\numpy which is not intended since -P is provided: https://github.com/numpy/numpy/issues/26816

Example of how -P option usually works

py -P new_test.py   
['C:\numpy\\build-install\\usr\\Lib\\site-packages', 'Python311\\python311.zip', 'Python311\\DLLs', 'Python311\\Lib', 'Python311', 'Python311\\Lib\\site-packages', 'Python311\\Lib\\site-packages\\win32', 'Python311\\Lib\\site-packages\\win32\\lib', 'Python311\\Lib\\site-packages\\Pythonwin']

Reproduce the Windows command py -P -m pytest new_test.py --capture=no and compare its sys.path with py -P new_test.py. Trace pytest's module entry point and startup path handling; done means pytest preserves Python's -P behavior so the current directory is not added to sys.path.