python 3.9: exciting/exciting.py: AttributeError: 'xml.etree.ElementTree.Element' object has no attribute 'getiterator'

https://bugzilla.redhat.com/show_bug.cgi?id=1792937

See https://copr-be.cloud.fedoraproject.org/results/@python/python3.9/fedora-rawhide-x86_64/01160984-python-ase/build.log.gz

This is hard to test since even Cython is broken with python 3.9 currently https://github.com/cython/cython/issues/3266, but apparently Fedora made some local patches and managed to advance to the build of ase itself.

See https://docs.python.org/3.9/whatsnew/3.9.html#removed

"Methods getchildren() and getiterator() in the ElementTree module have been removed. They were deprecated in Python 3.2. Use functions list() and iter() instead. The xml.etree.cElementTree module has been removed."