Fixing a regression with return_all_scores introduced in #17606 (#17906)

Fixing a regression with `return_all_scores` introduced in #17606

- The legacy test actually tested `return_all_scores=False` (the actual
  default) instead of `return_all_scores=True` (the actual weird case).

This commit adds the correct legacy test and fixes it.

Tmp legacy tests.

Actually fix the regression (also contains lists)

Less diffed code.

tests/pipelines/test_pipelines_text_classification.py

@@ -60,6 +60,29 @@ class TextClassificationPipelineTests(unittest.TestCase, metaclass=PipelineTestC
         outputs = text_classifier("This is great !", return_all_scores=False)
         self.assertEqual(nested_simplify(outputs), [{"label": "LABEL_0", "score": 0.504}])
 
+        outputs = text_classifier("This is great !", return_all_scores=True)
+        self.assertEqual(
+            nested_simplify(outputs), [[{"label": "LABEL_0", "score": 0.504}, {"label": "LABEL_1", "score": 0.496}]]
+        )
+
+        outputs = text_classifier(["This is great !", "Something else"], return_all_scores=True)
+        self.assertEqual(
+            nested_simplify(outputs),
+            [
+                [{"label": "LABEL_0", "score": 0.504}, {"label": "LABEL_1", "score": 0.496}],
+                [{"label": "LABEL_0", "score": 0.504}, {"label": "LABEL_1", "score": 0.496}],
+            ],
+        )
+
+        outputs = text_classifier(["This is great !", "Something else"], return_all_scores=False)
+        self.assertEqual(
+            nested_simplify(outputs),
+            [
+                {"label": "LABEL_0", "score": 0.504},
+                {"label": "LABEL_0", "score": 0.504},
+            ],
+        )
+
     @require_torch
     def test_accepts_torch_device(self):
         import torch