fix: release assets upload

[mayeut]

#267 introduced a regression in asset upload.

The layout of the artefacts to upload has changed. They're now all flatten in the working directory whereas before that PR, only the hashes.sha256 file was directly in the working directory. The change in layout caused .toString() to be called on python archives which corrupts the data that gets uploaded (as can be seen by comparing sha256 in hashes.sha256 with the ones from other uploaded assets).

This commit ensures that a "flat layout" is used and that toString() is only called for hashes.sha256.

[mayeut]

FYI: more debug runs in https://github.com/mayeut/python-versions/actions?query=branch%3Acheck-publish / https://github.com/mayeut/python-versions/blob/55b5d7a53a2da1db27d0bddbd86de071b9c6d8b4/.github/workflows/build-python-packages.yml#L199-L219

I'm not sure why toString() is needed in the first place but I'd rather do "same as before" rather than introduce a new regression.

A full build (including release publication) has been done, all files OK: https://github.com/mayeut/python-versions/actions/runs/9454191293

python-versions % curl -fsSLO https://github.com/mayeut/python-versions/releases/download/3.12.3-9454191293/hashes.sha256
python-versions % curl -fsSLO https://github.com/mayeut/python-versions/releases/download/3.12.3-9454191293/python-3.12.3-win32-x86.zip
python-versions % curl -fsSLO https://github.com/mayeut/python-versions/releases/download/3.12.3-9454191293/python-3.12.3-win32-x64.zip
python-versions % curl -fsSLO https://github.com/mayeut/python-versions/releases/download/3.12.3-9454191293/python-3.12.3-darwin-arm64.tar.gz
python-versions % curl -fsSLO https://github.com/mayeut/python-versions/releases/download/3.12.3-9454191293/python-3.12.3-darwin-x64.tar.gz
python-versions % curl -fsSLO https://github.com/mayeut/python-versions/releases/download/3.12.3-9454191293/python-3.12.3-linux-20.04-x64.tar.gz
python-versions % curl -fsSLO https://github.com/mayeut/python-versions/releases/download/3.12.3-9454191293/python-3.12.3-linux-22.04-x64.tar.gz
python-versions % curl -fsSLO https://github.com/mayeut/python-versions/releases/download/3.12.3-9454191293/python-3.12.3-linux-24.04-x64.tar.gz
python-versions % sha256sum -c hashes.sha256                            
python-3.12.3-darwin-arm64.tar.gz: OK
python-3.12.3-darwin-x64.tar.gz: OK
python-3.12.3-linux-20.04-x64.tar.gz: OK
python-3.12.3-linux-22.04-x64.tar.gz: OK
python-3.12.3-linux-24.04-x64.tar.gz: OK
python-3.12.3-win32-x64.zip: OK
python-3.12.3-win32-x86.zip: OK
python-versions % file python-3.12.3-*
python-3.12.3-darwin-arm64.tar.gz:    gzip compressed data, last modified: Mon Jun 10 19:13:32 2024, from Unix, original size modulo 2^32 45678592
python-3.12.3-darwin-x64.tar.gz:      gzip compressed data, last modified: Mon Jun 10 19:13:30 2024, from Unix, original size modulo 2^32 45678592
python-3.12.3-linux-20.04-x64.tar.gz: gzip compressed data, from Unix, original size modulo 2^32 395048960
python-3.12.3-linux-22.04-x64.tar.gz: gzip compressed data, from Unix, original size modulo 2^32 340613120
python-3.12.3-linux-24.04-x64.tar.gz: gzip compressed data, from Unix, original size modulo 2^32 339957760
python-3.12.3-win32-x64.zip:          Zip archive data, at least v2.0 to extract, compression method=deflate
python-3.12.3-win32-x86.zip:          Zip archive data, at least v2.0 to extract, compression method=deflate

[mayeut]

superseded by #286