Use python 3.8 in pytorch docker image (#45466)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/45466
Test Plan: Imported from OSS
Reviewed By: seemethere
Differential Revision: D23975294
Pulled By: tierex
fbshipit-source-id: 964de7928b541121963e9de792630bcef172bb5c
