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[hanhan761]

Summary

• update test_flag_group_competition_duplicate_option_name to assert the expected UserWarning explicitly
• assert the successful duplicate-option output when warnings are not promoted to errors

Issue

Fixes #3476

Verification

• PYTHONPATH=src python -m pytest -Wdefault tests/test_options.py::test_flag_group_competition_duplicate_option_name -q
• PYTHONPATH=src python -m pytest tests/test_options.py -q