[Paddle] Update _backends.py to support pir.Value (#353)

* Update _backends.py

"use paddle.is_tensor instead of isinstance to support pir.Value type"

* Update _backends.py

Author: HydrogenSulfate

einops/_backends.py

@@ -551,7 +551,7 @@ def __init__(self):
         self.paddle = paddle
 
     def is_appropriate_type(self, tensor):
-        return isinstance(tensor, (self.paddle.Tensor, self.paddle.static.Variable))
+        return self.paddle.is_tensor(tensor)
 
     def from_numpy(self, x):
         tensor = self.paddle.to_tensor(x)