Fix flaky nuclear_norm() test (#21638)
Summary:
Try to fix a sporadic failure on some CIs.
I've run this test hundreds of times on my machine (GeForce 1060, MAGMA) but I cannot reproduce this.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21638
Differential Revision: D15827779
Pulled By: ezyang
fbshipit-source-id: 3586075e48907b3b84a101c560a34cc733514a02
