[spmd] enable fully_shard fused_adam test (#99898)
This PR enables fully_shard fused adam tests with some additional tweaks
about how to handle scalar tensor. Now we treat scalar tensors as if
it's just a scalar value, we don't distribute it as there's no need to
shard a scalar tensor
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99898
Approved by: https://github.com/mrshenli
