Skip sccache initialization on MacOS (#99121)
Now that the cache is used on MacOS, I'm seeing some flaky timeout when starting the server https://github.com/pytorch/pytorch/actions/runs/4703387666/jobs/8341817701. This step is optional, so we could just skip it (like what Linux workflow does).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99121
Approved by: https://github.com/clee2000
