Replace squeeze with sum in _inf_max_helper (#2083)

Summary:
Pull Request resolved: #2083

This commit replaces `squeeze` with `sum` over length-1 dimensions in `_inf_max_helper` for PyTorch 1.13 compatibility.

Reviewed By: Balandat

Differential Revision: D51030343

fbshipit-source-id: 87ce5c5d71812a70553688d55c82aac56ddebbec

Author: SebastianAment

botorch/utils/safe_math.py

@@ -180,7 +180,11 @@ def _inf_max_helper(
         y_inf.sum(dim=dim, keepdim=True),
         M_no_inf + max_fun(y_no_inf, dim=dim, keepdim=True),
     )
-    return res if keepdim else res.squeeze(dim)
+    # NOTE: Using `sum` instead of `squeeze` because PyTorch < 2.0 does not support
+    # tuple `dim` arguments. `sum` and `squeeze` are equivalent here because the
+    # `dim` dimensions have length one after the reductions in the previous lines.
+    # TODO: Replace `sum` with `squeeze` once PyTorch >= 2.0 is required.
+    return res if keepdim else res.sum(dim=dim)
 
 
 def _any(x: Tensor, dim: Union[int, Tuple[int, ...]], keepdim: bool = False) -> Tensor: