Kwant tests fail on Python 3.8

Environment

• WSL2, Ubuntu 18.04
• Conda 4.8.2

What version was the error seen on?

v1.4.1, stable and master

Steps to reproduce

place conda-env.patch in the root of the Kwant repo, then:

git checkout stable
git apply conda-env.patch
conda env create -n kwant-latest -f docker/kwant-latest.yml
python setup.py build_ext --inplace
pytest kwant

prodcuces an error in test_builder.py:test_finalization:

kwant/tests/test_builder.py:388:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

fsyst = <kwant.builder.FiniteSystem object at 0x7f5ef126f850>
sites = {(0, 0): -0.17555375909487236, (0, 5): 0.0431815434225844, (0, 6): -0.4635004019048141, (0, 8): 0.4275265013095295, ...}
subset = False, check_values = True

    def check_onsite(fsyst, sites, subset=False, check_values=True):
        freq = {}
        for node in range(fsyst.graph.num_nodes):
            site = fsyst.sites[node].tag
            freq[site] = freq.get(site, 0) + 1
            if check_values and site in sites:
                assert fsyst.onsites[node][0] is sites[site]
        if not subset:
            # Check that all sites of `fsyst` are in `sites`.
            for site in freq.keys():
>               assert site in sites
E               assert array([0, 0]) in {(0, 0): -0.17555375909487236, (0, 5): 0.0431815434225844, (0, 6): -0.4635004019048141, (0, 8): 0.4275265013095295, ...}   
kwant/tests/test_builder.py:302: AssertionError