update CI script to take string docker image version (#31857)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31857
According to mingbowan we will change to use string docker image
version because the tag is no longer an integer since we move the docker
image build job to circle CI:
http://ossci-docker.s3-website.us-east-1.amazonaws.com/pytorch.html
Test Plan: - with stacked PR
Differential Revision: D19282726
Pulled By: ljk53
fbshipit-source-id: 7a12ae89a11cf15163b905734d50fed6dc98cb07
