cerbero package gstreamer-1.0 fails on Linux with python 3.9.1

Building GStreamer via cerbero package gstreamer-1.0 on Arch Linux with Python 3.9.1 installed fails at gobject-introspection:

cerbero/build/sources/linux_x86_64/gobject-introspection-1.56.1/./g-ir-scanner", line 66, in <module>
    sys.exit(scanner_main(sys.argv))
  File "./giscanner/scannermain.py", line 581, in scanner_main
    write_output(data, options)
  File "./giscanner/scannermain.py", line 469, in write_output
    passthrough_gir(main_f_name, temp_f)
  File "./giscanner/scannermain.py", line 259, in passthrough_gir
    parser.parse(path)
  File "./giscanner/girparser.py", line 64, in parse
    self.parse_tree(tree)
  File "./giscanner/girparser.py", line 73, in parse_tree
    self._parse_api(tree.getroot())
  File "./giscanner/girparser.py", line 110, in _parse_api
    for node in root.getchildren():
AttributeError: 'xml.etree.ElementTree.Element' object has no attribute 'getchildren'

Not sure why this fix hasn't been picked up? https://gitlab.gnome.org/GNOME/gobject-introspection/-/issues/325