Fix mypy.ini (#61333)
Summary:
Fixes CI regression caused by https://github.com/pytorch/pytorch/issues/61119
Unlike Python, `.ini` string lists could not end with trailing comma.
Fixes CI on master
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61333
Reviewed By: bhosmer
Differential Revision: D29578696
Pulled By: malfet
fbshipit-source-id: b81e5f4c0a553299c4d4bee0a9bb73748910795f
