fix sequence ci (#7644)

Author: lhoestq

src/datasets/features/features.py

@@ -1182,7 +1182,7 @@ class Sequence:
 
     def __new__(cls, feature=None, length=-1, **kwargs):
         # useful to still get isinstance(Sequence(Value("int64")), Sequence)
-        if isinstance(feature, dict):
+        if cls is Sequence and isinstance(feature, dict):
             out = {key: List(value, length=length, **kwargs) for key, value in feature.items()}
         else:
             out = super().__new__(List)