Address torch.tensor warnings in derivative sensitivity measures (#2378)

Summary:
Eliminates 5 instances of the following warning in tests:
```
UserWarning: To copy construct from a tensor, it is recommended to use sourceTensor.clone().detach() or sourceTensor.clone().detach().requires_grad_(True), rather than torch.tensor(sourceTensor).
```

Pull Request resolved: #2378

Reviewed By: Balandat

Differential Revision: D56314211

Pulled By: saitcakmak

fbshipit-source-id: 6466a55f61dd60085896c4bcd27b8ddacb8cd933

ax/utils/sensitivity/derivative_measures.py

@@ -168,7 +168,7 @@ def gradient_measure(self) -> torch.Tensor:
             else
                 Tensor: (values) x dim
         """
-        return self.aggregation(torch.tensor)
+        return self.aggregation(torch.as_tensor)
 
     def gradient_absolute_measure(self) -> torch.Tensor:
         r"""Computes the gradient absolute measure: