gpgmepy: Broken sdist build

[Paul Schwabauer]

I recently tried building a Python source distribution for |gpgmepy| 
using either |python setup.py sdist| or |make sdist| from the build 
directory. However, the resulting source tarball is incomplete; it’s 
missing several necessary files.

You can verify this by running |python -m build|, which builds the 
package in an isolated environment and highlights the missing components.

To work around this issue, I had to follow the approach described here: 
https://issues.roundup-tracker.org/msg8362. Unfortunately, due to the 
custom nature of |gpgmepy|'s build process, I haven't found a clean way 
to integrate this fix without potentially disrupting workflows that the 
package maintainers rely on.

One complication is that |setuptools| requires the |MANIFEST.in| file, 
and the files it references, to be present in the current working 
directory during packaging.

If anyone has insights into the |gpgmepy| build process or suggestions 
for integrating a more robust solution, I'd really appreciate the help.