[BE] Move `setup-ssh` step ahead of clone PyTorch (#88715)
It allows one to SSH faster rather than having to wait for repo clone to
finish.
I.e. right now one usually have to wait for a few minutes fore PyTorch clone is finished, but with this change you can SSH ahead of time (thanks to `setup-ssh` being a composite action
Pull Request resolved: https://github.com/pytorch/pytorch/pull/88715
Approved by: https://github.com/clee2000, https://github.com/izaitsevfb
