macOS release should not have a zip inside another zip

[Fabxx]

by default the macOS release should have a single .zip containing melonDS.app folder.

When trying to extract zip in the same folder, programs such as 7z or unzip ask to overwrite the existing archive, resulting in a extraction failure.

[nadiaholmquist]

There's not really a good way to get around this. GitHub Actions will zip any file you upload, even if the file itself is a zip, and we need to compress it ourselves because GitHub's zipping does not preserve file permissions, which are needed to make the executable actually executable.