Add torch.bincount() test case on sliced tensor (#15835)
Summary:
This was causing a problem in #15735 but appears to have been fixed.
Adding this test to prevent regressions.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15835
Differential Revision: D13600282
Pulled By: zou3519
fbshipit-source-id: d9939e74d372be71c50122a5f6a615fbd7fa4df6
