Add dill>=0.3.1 as testing dependency (#31121)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31121
For https://github.com/pytorch/pytorch/pull/30985 .
Test Plan:
- run `pip install "dill>=0.3.1"` locally, check that it actually
installs dill>=0.3.1.
Differential Revision: D18934871
Pulled By: zou3519
fbshipit-source-id: 688a489b9e81134ccb5ab4b099116e3fe6b6b7ae
