Fix Windows python3 path (#93387)
If a Windows runner is re-used, python3 should have already been setup. We will just need to make it available in `GITHUB_PATH`, so subsequent actions can use it
Pull Request resolved: https://github.com/pytorch/pytorch/pull/93387
Approved by: https://github.com/clee2000, https://github.com/malfet, https://github.com/seemethere
