Reenable `isinstance` with `torch.distributed.ReduceOp` (#87303)
tentatively marking as draft as I haven't gotten a comprehensive list of side effects...
Ref: https://stackoverflow.com/questions/40244413/python-static-class-attribute-of-the-class-itself
Rel: https://github.com/pytorch/pytorch/issues/87191
cc @kwen2501
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87303
Approved by: https://github.com/wanchaol
