chore(actions): flattens the wheel atrifacts upload

... instead of python-platform specific dirs - like
"cibw-wheels-cp313-manylinux_x86_64/" for instance - we put the files at
the root, which should put them all side-by-side and reduce the amount
of wrangling we need to do later.

.github/workflows/wheels.yml

@@ -58,7 +58,6 @@ jobs:
 
       - uses: actions/upload-artifact@v4
         with:
-          name: cibw-wheels-${{ matrix.only }}
           path: ./wheelhouse/*.whl
 
   collate-wheels: