Fixing the enum related failing test under python 3.11 (#1402)

# Description

This is to fixing the failing test: test_reference_code under python
3.11

# All Promptflow Contribution checklist:
- [x] **The pull request does not introduce [breaking changes].**
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significant changes.**
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### Testing Guidelines
- [x] Pull request includes test coverage for the included changes.

src/promptflow/tests/executor/unittests/_utils/test_exception_utils.py

@@ -624,10 +624,10 @@ def test_reference_code(self):
             raise_tool_execution_error()
 
         e = e.value
-        assert e.reference_code == ErrorTarget.TOOL
+        assert e.reference_code == ErrorTarget.TOOL.value
         module = "promptflow_vectordb.tool.faiss_index_loopup"
         e.module = module
-        assert e.reference_code == f"{ErrorTarget.TOOL}/{module}"
+        assert e.reference_code == f"{ErrorTarget.TOOL.value}/{module}"
 
     @pytest.mark.parametrize(
         "func_that_raises_exception",