fix: Ensure group tasks are deeply deserialised

Fixes #6341

celery/canvas.py

@@ -1028,8 +1028,9 @@ class group(Signature):
 
     @classmethod
     def from_dict(cls, d, app=None):
+        tasks = [maybe_signature(task) for task in d["kwargs"]["tasks"]]
         return _upgrade(
-            d, group(d['kwargs']['tasks'], app=app, **d['options']),
+            d, group(tasks, app=app, **d['options']),
         )
 
     def __init__(self, *tasks, **options):

t/unit/tasks/test_canvas.py

@@ -633,15 +633,13 @@ def test_from_dict(self):
         x['args'] = None
         assert group.from_dict(dict(x))
 
-    @pytest.mark.xfail(reason="#6341")
     def test_from_dict_deep_deserialize(self):
         original_group = group([self.add.s(1, 2)] * 42)
         serialized_group = json.loads(json.dumps(original_group))
         deserialized_group = group.from_dict(serialized_group)
         for ds_task in deserialized_group.tasks:
             assert isinstance(ds_task, Signature)
 
-    @pytest.mark.xfail(reason="#6341")
     def test_from_dict_deeper_deserialize(self):
         inner_group = group([self.add.s(1, 2)] * 42)
         outer_group = group([inner_group] * 42)
@@ -859,7 +857,6 @@ def test_from_dict_deep_deserialize(self):
             assert isinstance(task, Signature)
         assert isinstance(deserialized_chord.body, Signature)
 
-    @pytest.mark.xfail(reason="#6341")
     def test_from_dict_deep_deserialize_group(self):
         header = body = group([self.add.s(1, 2)]* 42)
         original_chord = chord(header=header, body=body)
@@ -874,7 +871,6 @@ def test_from_dict_deep_deserialize_group(self):
         for task in deserialized_chord.body.tasks:
             assert isinstance(task, Signature)
 
-    @pytest.mark.xfail(reason="#6341")
     def test_from_dict_deeper_deserialize_group(self):
         inner_group = group([self.add.s(1, 2)] * 42)
         header = body = group([inner_group] * 42)