core[patch]: fix xml output parser transform (#19530)

Previous PR passed _parser attribute which apparently is not meant to be
used by user code and causes non deterministic failures on CI when
testing the transform and a transform methods. Reverting this change
temporarily.

libs/core/tests/unit_tests/output_parsers/test_xml_parser.py

@@ -1,6 +1,5 @@
 """Test XMLOutputParser"""
 from typing import AsyncIterator
-from xml.etree.ElementTree import ParseError
 
 import pytest
 
@@ -100,17 +99,3 @@ async def tests_billion_laughs_attack() -> None:
 
     with pytest.raises(OutputParserException):
         await parser.aparse(MALICIOUS_XML)
-
-    with pytest.raises(ParseError):
-        # Right now raises undefined entity error
-        assert list(parser.transform(iter(MALICIOUS_XML))) == [
-            {"foo": [{"bar": [{"baz": None}]}]}
-        ]
-
-    async def _as_iter(string: str) -> AsyncIterator[str]:
-        for c in string:
-            yield c
-
-    with pytest.raises(ParseError):
-        chunks = [chunk async for chunk in parser.atransform(_as_iter(MALICIOUS_XML))]
-        assert chunks == [{"foo": [{"bar": [{"baz": None}]}]}]