Add missing scalar example in docs of `torch.where` (#93145)
[`torch.where(condition, x, y)`](https://pytorch.org/docs/stable/generated/torch.where.html) accepts `x` and `y` as either `Tensor` or Scalar, but the Scalar example is missing in the docs. I simply add the example.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/93145
Approved by: https://github.com/ngimel
