`--pyargs` broken in Python 3.14.2 in tox

This issue only presents when using pytest in tox, for some reason, and only when tox tests Python 3.14.2.

I have a project laid out like this:

pytesttest
├── amodule
│   ├── __init__.py
│   └── tests
│       ├── __init__.py
│       └── test_some.py
└── tox.ini

When I run tox run, I get:

============================= test session starts ==============================
platform linux -- Python 3.14.2, pytest-9.0.2, pluggy-1.6.0
cachedir: .tox/py314/.pytest_cache
rootdir: /home/sanotehu/src/pytesttest
collected 0 items                                                              

============================ no tests ran in 0.00s =============================
ERROR: module or package not found: amodule.tests (missing __init__.py?)

py314: exit 4 (0.33 seconds) /home/sanotehu/src/pytesttest> pytest --pyargs amodule.tests pid=951849
  py314: FAIL code 4 (3.70=setup[3.37]+cmd[0.33] seconds)
  evaluation failed :( (3.72 seconds)

But if I go to some other Python 3.14.2 virtualenv and run pytest --pyargs amodule.tests, the test passes. Usually. I might have to run pyclean --debris=all first.

Contents of test_some.py:

def test_something():
	print("Hello, world!")

Contents of tox.ini:

[tox]
envlist = py314

[testenv]
deps = pytest
commands = pytest --pyargs amodule.tests

Output of pip list:

Package       Version
------------- -------
cachetools    6.2.4
chardet       5.2.0
colorama      0.4.6
distlib       0.4.0
filelock      3.20.1
packaging     25.0
pip           24.0
platformdirs  4.5.1
pluggy        1.6.0
pyproject-api 1.10.0
tox           4.32.0
virtualenv    20.35.4

I filed the same issue in tox, since I can't tell which is responsible.

Start by reproducing the pytest --pyargs amodule.tests command from the reported tox.ini on Python 3.14.2, comparing the tox environment with the standalone virtualenv. Inspect how --pyargs resolves amodule.tests and use test_some.py as the success case. Done means the tox invocation collects and runs the test reliably.