fix: Remove unused mock_trainer variable in test

- Removed unused mock_trainer variable in test_deploy_new_model_validation_failed
- Resolves Ruff F841 error about unused variable assignment
- All Ruff checks now pass cleanly

Author: RuiFSP

tests/integration/test_retraining_flow.py

@@ -283,8 +283,6 @@ def test_deploy_new_model_validation_failed(self):
             model_file_path = Path(temp_dir) / "temp_model.pkl"
             model_file_path.write_text("dummy model")
 
-            mock_trainer = Mock()
-
             validation_results = {
                 "should_deploy": False,
                 "new_accuracy": 0.40,