asdf.open leaves behind an open file if it can't sort out how to open it

[jdavies-st]

The following test illustrates:

# test_open_fail.py

from pathlib import Path

import asdf
import pytest


def test_asdf(tmp_path):
    path = tmp_path / "empty.asdf"
    Path(path).touch()

    with asdf.open(path) as af:
        pass

When run with pytest test_open_fail.py --open-files, the test fails as expected with

E           ValueError: Input object does not appear to be an ASDF file or a FITS with ASDF extension

But also produces a teardown error, since it leaves the file open:

E           AssertionError: File(s) not closed:
E             /private/var/folders/jg/by5st33j7ps356dgb4kn8w900001n5/T/pytest-of-jdavies/pytest-157/test_asdf0/empty.asdf