Add test to lerp function (#42266)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42266
function `lerp_kernel_scalar` and `lerp_kernel_tensor` are not covered in `Aten/native/cpu/LerpKernel.cpp`, add tests to cover them
Test Plan:
1. Test locally to check new lines are covered
2. CI
https://pxl.cl/1fXPd
Reviewed By: malfet
Differential Revision: D22832164
fbshipit-source-id: b1eaabbf8bfa08b4dedc1a468abfdfb619a50e3c
