don't overspecify required python version (#28842)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28842
We don't care which python version, and github actions has changed the
versions available, breaking our CI. So just pin it to 3-something to
make it more future proof
Test Plan: Imported from OSS
Differential Revision: D18205349
Pulled By: suo
fbshipit-source-id: bf260dc29a138dd8bf8c85081a182aae298fe86d
