Bump up NCCL to v2.8 (#46742)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46742
Use NCCL v2.8
Test Plan: waitforsandcastle
Reviewed By: mrshenli
Differential Revision: D24488800
fbshipit-source-id: d39897da1499e63ca783a81aec1ce707606423a3
