std/var: support floating point correction value (#94073)
Ref https://github.com/pytorch/pytorch/issues/61492#issuecomment-1413003480
The array API specifies correction to be `Union[int, float]` while we currently only support integers.
https://data-apis.org/array-api/latest/API_specification/generated/array_api.std.html
As std/var is calculated currently, the final count of elements is already done
in floating point so we can make the correction floating point without any loss
of precision or generality.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/94073
Approved by: https://github.com/ezyang
