Fix issue with twine 6.1.0

[julienr]

Twine 6.1.0 was released on Jan 21 (yesterday) and we now have master builds failing with

removing 'build/bdist.linux-x86_64/dumb' (and everything under it)
Checking dist/picterra-2.0.5.linux-x86_64.tar.gz: ERROR    InvalidDistribution: Too many top-level members in sdist archive:      
         {self.filename}                         

I can reproduce this locally with twine==6.1.0. Downgrading to twine==6.0.1 fixes the issue.

I'll downgrade as a workaround to unblock CI, but we should investigate what this is about.