devel/py-setuptools_scm: Update to 6.4.2

• Fold the TOML option because its dependency is no longer an optional requirement as noted in "setup.{py,cfg}". This should also fix some cases with build errors where the TOML option was disabled. [1]

Changelog since 6.3.2:

https://github.com/pypa/setuptools_scm/blob/v6.4.2/CHANGELOG.rst

PR: 259797 [1], 261698 [1]
MFH: No (feature release)