LICENSE file is missing in 20.5 pypi release

```
# cat packaging/__init__.py
# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.
```
but named file is not shipped with packaging-20.5.tar.gz.
That was different for 20.4 releases
