[pthreadpool] Don't recreate threadpool if the counts are same (#90478)
Summary: Don't do anything if the incoming count and current threadpool size are same
Test Plan: CI
Reviewed By: salilsdesai
Differential Revision: D41628132
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90478
Approved by: https://github.com/salilsdesai
