test_seek is broken on FreeBSD

[ligurio]

setup_unreliablefs = ('/tmp/pytest-of-root/pytest-0/test_seek0/mnt', '/tmp/pytest-of-root/pytest-0/test_seek0/src')

    def test_seek(setup_unreliablefs):
        mnt_dir, src_dir = setup_unreliablefs
        name = name_generator()
        os_create(pjoin(src_dir, name))
        fullname = pjoin(mnt_dir, name)
        with os_open(fullname, os.O_WRONLY) as fd:
            os.lseek(fd, 1, os.SEEK_SET)
>           os.write(fd, b'foobar\n')
E           OSError: [Errno 9] Bad file descriptor

tests/test_unreliablefs.py:200: OSError

https://cirrus-ci.com/task/5170998354903040?command=test#L47