[Caffe2][Pruning] Make the caffe2 Sum operator support long types (#40379)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40379
The current sum operator doesn't support Long .. hence modify the code
Test Plan: Write a test case
Reviewed By: jspark1105, yinghai
Differential Revision: D21917365
fbshipit-source-id: b37d2c100c70d17d2f89c309e40360ddfab584ee
