Python -00 test is fragile to PATH
https://github.com/pandas-dev/pandas/blob/ab668b0a56a9f2aee959bde787e9a0af4068d7a7/pandas/tests/test_downstream.py#L60

that assumes that first `python`  on the PATH is the one running the tests, which it may not be (e.g. if doing `./venv/bin/python`

We should replace `python` with something like `sys.executable`.