Numpy deprecation warning (#2037)

Summary:
This gets rid of the following warning: `DeprecationWarning: Conversion of an array with ndim > 0 to a scalar is deprecated, and will error in future.`

Pull Request resolved: #2037

Reviewed By: Balandat

Differential Revision: D49992423

Pulled By: dme65

fbshipit-source-id: 885f2a43c758e0a0cab5cbd5111a1a90fcc73d99

botorch/models/model.py

@@ -427,7 +427,7 @@ def _get_group_subset_indices(
         idcs = [idx % cum_output_sizes[-1] for idx in idcs]
         group_indices: Dict[int, List[int]] = defaultdict(list)
         for idx in idcs:
-            grp_idx = int(np.argwhere(idx < cum_output_sizes)[0])
+            grp_idx = np.argwhere(idx < cum_output_sizes)[0].item()
             sub_idx = idx - int(np.sum(output_sizes[:grp_idx]))
             group_indices[grp_idx].append(sub_idx)
         return group_indices