GH Actions: bump actions/upload-artifact to v7 (was v4)

Despite several major version bumps, there should be no breaking
changes. The only notable change is that
https://github.com/actions/upload-artifact/releases/tag/v6.0.0 runs on
Node.js 24 (unlike v5.0.0, which still ran on Node.js 20).

Author: generalmimon

.github/workflows/release.yml

@@ -27,7 +27,7 @@ jobs:
       - name: Build a binary wheel and a source tarball
         run: python3 -m build
       - name: Store the package distributions
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v7
         with:
           name: python-package-distributions
           path: dist/