Fix path handling on Win32 in rendezvous.py (#57000)
Summary:
Fixes test failure after https://github.com/pytorch/pytorch/issues/56598
Introduced by https://github.com/pytorch/pytorch/issues/45335.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57000
Reviewed By: zou3519
Differential Revision: D28030360
Pulled By: seemethere
fbshipit-source-id: 4871d51e6b80dceef8bf95c6c658441287575f63
