pyproject: Ensure sources.json is installed by setuptools.

[nicolas-graves]

I couldn't build the package from source on Gnu Guix without ensuring the sources.json file is there.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.87%. Comparing base (473f3af) to head (1a4ca5b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #185      +/-   ##
==========================================
- Coverage   98.91%   97.87%   -1.04%     
==========================================
  Files          95       95              
  Lines        7539     7539              
==========================================
- Hits         7457     7379      -78     
- Misses         82      160      +78     

see 18 files with indirect coverage changes

[khaeru]

The repo uses a reusable workflow (this one) to confirms that package can be built properly. Here you can see that it picks up sources.json. This is also the workflow used to push tags (release candidates) and new releases to PyPI. You can also confirm that the releases on PyPI include the file.

Can you please:

1. Explain which tool(s) (including versions) and exact command(s) you were using to attempt to build and/or install the package, and
2. Show the complete output?