`ImportPathMismatchError` from subprojects with same test folder structure

We have a big CI job that runs pytest against a couple (sub)projects checked out side by side. We added a __init__.py file in one of the tests folders to allow for some internal code reuse, and now the whole test suite fails to run with a ImportPathMismatchError.

Minimal reproduction example:

cd some_empty_root_dir
mkdir -p projectA/tests
touch projectA/tests/__init__.py
touch projectA/tests/conftest.py
mkdir -p projectB/tests
touch projectB/tests/__init__.py
touch projectB/tests/conftest.py

So file structure is as follows

$ tree
.
├── projectA
│   └── tests
│       ├── conftest.py
│       └── __init__.py
└── projectB
    └── tests
        ├── conftest.py
        └── __init__.py

Running pytest in each of the subprojects works fine (collected 0 items, but that is expected).

However, when running at the toplevel:

$ pytest
=============================================================================================== test session starts ===============================================================================================
platform linux -- Python 3.11.0, pytest-7.4.0, pluggy-1.2.0
rootdir: /tmp/fruplz
collected 0 items / 1 error                                                                                                                                                                                       

===================================================================================================== ERRORS ======================================================================================================
__________________________________________________________________________________________ ERROR collecting test session __________________________________________________________________________________________
.venv/lib/python3.11/site-packages/_pytest/config/__init__.py:642: in _importconftest
    mod = import_path(conftestpath, mode=importmode, root=rootpath)
.venv/lib/python3.11/site-packages/_pytest/pathlib.py:588: in import_path
    raise ImportPathMismatchError(module_name, module_file, path)
E   _pytest.pathlib.ImportPathMismatchError: ('tests.conftest', '/tmp/fruplz/projectA/tests/conftest.py', PosixPath('/tmp/fruplz/projectB/tests/conftest.py'))
============================================================================================= short test summary info =============================================================================================
ERROR  - _pytest.pathlib.ImportPathMismatchError: ('tests.conftest', '/tmp/fruplz/projectA/tests/conftest.py', PosixPath('/tmp/fruplz/projectB/tests/conftest.py'))
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
================================================================================================ 1 error in 0.04s =================================================================================================

Apparently pytest doesn't like that both projectA/tests/conftest.py and projectB/tests/conftest.py map to tests.conftest.
Is there a workaround for this?

(using pytest 7.4.0)

Reproduce the failure with the projectA/projectB layout and top-level pytest invocation shown in the issue. Start by tracing the reported _pytest/config/init.py and _pytest/pathlib.py locations to understand how both conftest.py files resolve to tests.conftest. Done means providing a tested fix or documented workaround for side-by-side subprojects.