[FR] Relax validation of py-modules

[abravalheri]

The pip-run project defines a py-module that has a dash in the name. It does so intentionally in order to make it possible to type python -m pip-run without having to enter any chorded characters (- is roughly 1/3 as expensive as _).

After converting the config to pyproject.toml, however, this value is rejected by policy.

ValueError: invalid pyproject.toml config: `tool.setuptools.py-modules[0]`.
configuration error: `tool.setuptools.py-modules[0]` must be python-module-name
Backend: run command get_requires_for_build_editable with args {'config_settings': None}
configuration error: `tool.setuptools.py-modules[0]` must be python-module-name
GIVEN VALUE:
    "pip-run"

OFFENDING RULE: 'format'

DEFINITION:
    {
        "type": "string",
        "format": "python-module-name"
    }

I can understand why "python-module-name" seemed like a good reasonableness check, but it turns out to be backward incompatible and unnecessarily constraining against a use-case like above.

Can we back out this change and make it lenient as it was with setup.cfg?

@jaraco in pypa/setuptools#4316