* [PyPI] Fix license for packages following PEP 639
PEP 639 states that the preferred way of documenting a Python project's
license is an SPDX expression in a `License-Expression` metadata field.
PyPI exposes this information in `info.license_expression` in its JSON
data.
Fixes: #11000
* add license_expression to pypi response schema
* move comments inline into the relevant blocks
* assign both license and license_expression to intermediate variables
* always pass a license_expression in test input objects
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Co-authored-by: chris48s <git@chris-shaw.dev>