tests/comparators/test_directory.py: non-deterministic failure on guix

With diffoscope versions 126+, I've started seeing occasional test failures building diffoscope on guix, though usually works after a couple build attempts.

I haven't tracked the issue down yet weather it's something in guix (which is a fairly fast-moving target) or in diffoscope, but figured I'd report the issue at least in case something obvious jumps out at someone else:

=================================== FAILURES ===================================
_________________________________ test_content _________________________________

differences = [<Difference /gnu/store/9kzrrccpzl6i1sfwb0drb00gi2gwk0x0-coreutils-8.31/bin/stat {} -- /gnu/store/
9kzrrccpzl6i1sfwb0dr...00gi2gwk0x0-coreutils-8.31/bin/stat {} -- /gnu/store/9kzrrccpzl6i1sfwb0drb00gi2gwk0x0-cor
eutils-8.31/bin/stat {} []>]>]

    def test_content(differences):
>       assert differences[0].source1 == 'dir'
E       AssertionError: assert '/gnu/store/9...1/bin/stat {}' == 'dir'
E         - /gnu/store/9kzrrccpzl6i1sfwb0drb00gi2gwk0x0-coreutils-8.31/bin/stat {}
E         + dir

tests/comparators/test_directory.py:70: AssertionError
============== 1 failed, 367 passed, 56 skipped in 93.84 seconds ===============
command "python" "-c" "import setuptools, tokenize;__file__='setup.py';f=getattr(tokenize, 'open', open)(__file_
_);code=f.read().replace('\\r\\n', '\\n');f.close();exec(compile(code, __file__, 'exec'))" "test" failed with st
atus 1