Description of problem:
Package pybind11 fails to build from source in Fedora rawhide with Python 3.8.0rc1:

_____________________________ test_class_refcount ______________________________
    @pytest.unsupported_on_pypy
    def test_class_refcount():
        """Instances must correctly increase/decrease the reference count of their types (#1029)"""
        from sys import getrefcount
    
        class PyDog(m.Dog):
            pass
    
        for cls in m.Dog, PyDog:
            refcount_1 = getrefcount(cls)
            molly = [cls("Molly") for _ in range(10)]
            refcount_2 = getrefcount(cls)
    
            del molly
            pytest.gc_collect()
            refcount_3 = getrefcount(cls)
    
>           assert refcount_1 == refcount_3
E           assert 6 == 16
test_class.py:255: AssertionError

Version-Release number of selected component (if applicable):
2.4.2-1.fc32

Steps to Reproduce:
koji build --scratch f32 pybind11-2.4.2-1.fc32.src.rpm

Additional info:
This package is tracked by Koschei. See:
http://koschei.fedoraproject.org/package/pybind11