bug#54899: Add version metadata check to Python sanity-check

[Maxim Cournoyer]

Hello Guix,

Many Python packages rely on third party packages such as
python-setuptools-scm or python-versioneer to compute the version string
used as part of the packaging.

When these tools are missing, the version string ends up being '0.0.0'
in the resulting PKG-INFO package metadata file, which is wrong and
breaks Python build systems dependency verification.

This issue is about adding a check to our already existing sanity-check
phase/script so that it ensure the version string in the built package
metadata is not 0.0.0 (unless defined as such at the level of the Guix
package).

Thanks,

Maxim