pplpy*: update upstream info and deps

[dimpase]

📚 pplpy/pplpy_doc: update upstream info and deps

these are now hosted on sagemath;
also, build system of pplpy errors out if there is no sphinx.

📝 Checklist

• I have made sure that the title is self-explanatory and the description concisely explains the PR.

[github-actions]

Documentation preview for this PR is ready! 🎉
Built with commit: 9a30251

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -0.02 ⚠️

Comparison is base (f449b14) 88.62% compared to head (9a30251) 88.61%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #35289      +/-   ##
===========================================
- Coverage    88.62%   88.61%   -0.02%     
===========================================
  Files         2148     2148              
  Lines       398653   398653              
===========================================
- Hits        353308   353268      -40     
- Misses       45345    45385      +40     

see 25 files with indirect coverage changes

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