Fix default behaviour in TextClassificationPipeline for regression problem type (#34066)

* update code

* update docstrings

* update tests

tests/pipelines/test_pipelines_text_classification.py

@@ -108,6 +108,12 @@ class TextClassificationPipelineTests(unittest.TestCase):
             ],
         )
 
+        # Do not apply any function to output for regression tasks
+        # hack: changing problem_type artifically (so keep this test at last)
+        text_classifier.model.config.problem_type = "regression"
+        outputs = text_classifier("This is great !")
+        self.assertEqual(nested_simplify(outputs), [{"label": "LABEL_0", "score": 0.01}])
+
     @require_torch
     def test_accepts_torch_device(self):
         text_classifier = pipeline(