[caffe2] add tests for inplace elementwise ops (#60106)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60106
In Caffe2, some elementwise in-place compatible ops lack coverage for the in-place case. We add tests for a subset of them here and thereby increase coverage.
Test Plan:
```
buck test //caffe2/caffe2/python/operator_test:elementwise_ops_test
```
Let CI run.
Reviewed By: clrfb
Differential Revision: D29143189
fbshipit-source-id: 83138ad8eff8fe95c40aece53714da3577396a23
