Not allowing DTDs breaks the OJAudit source

[fniessink]

Traceback (most recent call last):
  File "/home/collector/base_collectors/source_collector.py", line 142, in __safely_parse_source_responses
    measurement = await self._parse_source_responses(responses)
  File "/home/collector/source_collectors/file_source_collectors/ojaudit.py", line 27, in _parse_source_responses
    tree, namespaces = await parse_source_response_xml_with_namespace(response)
  File "/home/collector/collector_utilities/functions.py", line 27, in parse_source_response_xml_with_namespace
    tree = await parse_source_response_xml(response, allowed_root_tags)
  File "/home/collector/collector_utilities/functions.py", line 18, in parse_source_response_xml
    tree = cast(Element, ElementTree.fromstring(await response.text(), forbid_dtd=True))
  File "/usr/local/lib/python3.9/site-packages/defusedxml/common.py", line 131, in fromstring
    parser.feed(text)
  File "/usr/local/lib/python3.9/xml/etree/ElementTree.py", line 1720, in feed
    self.parser.Parse(data, False)
  File "/usr/src/python/Modules/pyexpat.c", line 671, in StartDoctypeDecl
  File "/usr/local/lib/python3.9/site-packages/defusedxml/ElementTree.py", line 108, in defused_start_doctype_decl
    raise DTDForbidden(name, sysid, pubid)
defusedxml.common.DTDForbidden: DTDForbidden(name='audit', system_id=None, public_id=None)