Coerce Distribution.script_args to list

[Avasam]

This will allow any iterable to be passed as script_args for setup.
After this is merged, typeshed can be updated to reflect this change, which will allow https://github.com/jaraco/jaraco.office/pull/2/files#diff-bb91dce3f1ce94166001a97817fed8d6a6a56c6d7f95233cc28268aea7f05778R24 to pass.

If you don't want the coercion, then script_args should at least be typed as Sequence[str] and python/typeshed#13116 should be merged first.

I also noticed, I think there's no validation that script_args isn't a plain str