up Pytorch version for PyPI (#568)

Summary:
Deploy failed due to unavailable Python

https://github.com/pytorch/opacus/actions/runs/4241660361

Pull Request resolved: #568

Reviewed By: karthikprasad

Differential Revision: D43494621

Pulled By: ffuuugor

fbshipit-source-id: d8ae67e0133ee963715b34966ae7193156def309

.github/workflows/python-publish.yml

@@ -17,7 +17,7 @@ jobs:
     - name: Set up Python
       uses: actions/setup-python@v2
       with:
-        python-version: '3.7.5'
+        python-version: '3.8'
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip