test(models): re-enable finish_reason unknown-maps-to-OTHER litellm test

test_finish_reason_unknown_maps_to_other was skipped during the v2.0.0 GA
transition with reason "LiteLLM finish_reason mapping behaviour changed".
That reason is now stale: _map_finish_reason ends with
_FINISH_REASON_MAPPING.get(finish_reason_str, types.FinishReason.OTHER), so
any unmapped finish_reason deterministically maps to OTHER regardless of
LiteLLM's own normalization. The test bypasses that normalization with a mock
returning a raw "totally_unknown_reason" and asserts the OTHER fallback.

This skipped test is the only coverage of the _map_finish_reason -> OTHER
fallback branch in the litellm suite, so the skip left a live production
branch untested. Removing the skip restores that coverage with no production
change; the test passes as-is.

Author: anxkhn

tests/unittests/models/test_litellm.py

@@ -4984,7 +4984,6 @@ def test_model_response_to_generate_content_response_safety_finish_reason():
   assert llm_response.error_message == "Finished with SAFETY"
 
 
-@pytest.mark.skip(reason="LiteLLM finish_reason mapping behaviour changed")
 @pytest.mark.asyncio
 async def test_finish_reason_unknown_maps_to_other(
     mock_acompletion, lite_llm_instance