fix(mge/tensor): fix is/is not SyntaxWarning occurs in python3.8

GitOrigin-RevId: 12b66da3675b6e418b161e7c301e40ca8302ea9f

imperative/python/megengine/functional/tensor.py

@@ -134,7 +134,7 @@ def full(shape, value, dtype="float32", device=None) -> Tensor:
     if device is None:
         device = get_default_device()
     (x,) = Const(value, dtype=dtype, device=device)()
-    if shape is ():  # scalar.shape
+    if type(shape) in (list, tuple) and len(shape) == 0:
         return x
     return broadcast_to(x, shape)
 
@@ -278,7 +278,7 @@ def full_like(
 
     """
     (x,) = Const(value, dtype=inp.dtype, device=inp.device)(inp)
-    if inp.shape is ():
+    if inp.ndim == 0:
         return x
     return broadcast_to(x, inp.shape)