feature: Set Private :: Do Not Upload trove classifier in Insiders versions?

[pawamoy]

This classifier makes PyPI rejects uploads (additional safety to prevent releasing private versions to PyPI). However we should make sure other registries (like pypiserver!) don't do the same thing: users must be able to publish the built sdist/wheel to their private registries.

[pawamoy]

Quoting official docs:

To prevent a package from being uploaded to PyPI, use the special "Private :: Do Not Upload" classifier. PyPI will always reject packages with classifiers beginning with "Private ::".

• https://pypi.org/classifiers/
• https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#classifiers

Unfortunately, they don't tell if this is a PyPI-only thing. The original PEP (https://peps.python.org/pep-0301/#distutils-trove-classification) doesn't mention such classifiers. So that leaves the official docs up to interpretation by those who implement Python packages registries 🤔