use torch.where over boolean masking (#8171)

torchvision/transforms/v2/functional/_geometry.py

@@ -595,8 +595,7 @@ def _apply_grid_transform(img: torch.Tensor, grid: torch.Tensor, mode: str, fill
         fill_list = fill if isinstance(fill, (tuple, list)) else [float(fill)]  # type: ignore[arg-type]
         fill_img = torch.tensor(fill_list, dtype=float_img.dtype, device=float_img.device).view(1, -1, 1, 1)
         if mode == "nearest":
-            bool_mask = mask < 0.5
-            float_img[bool_mask] = fill_img.expand_as(float_img)[bool_mask]
+            float_img = torch.where(mask < 0.5, fill_img.expand_as(float_img), float_img)
         else:  # 'bilinear'
             # The following is mathematically equivalent to:
             # img * mask + (1.0 - mask) * fill = img * mask - fill * mask + fill = mask * (img - fill) + fill