[BE]: Update NCCL submodule to v2.19.3 (#110827)
Updates NCCL submodule to v2.19.3 Mostly contains some more performance fixes for H100s as well as a couple new performance features and some new plugin support.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/110827
Approved by: https://github.com/malfet
