Correct var_mean in _refs/__init__.py (#78971)
I've found this by looking at https://lgtm.com/projects/g/pytorch/pytorch/
Maybe there is value in lgtm.com integration, as proposed in https://github.com/pytorch/pytorch/issues/78425
Pull Request resolved: https://github.com/pytorch/pytorch/pull/78971
Approved by: https://github.com/ngimel
