Restore correct macos build upload in CI

Our macOS export exports two files. There's a zip file containing an app package that can be ran by the user directly and a DMG file. Before we were uploading the DMG file, which didn't work anymore for users in the latest versions. We took that down.

Now instead, we want to take the zipped package, which is already the application pre-packaged and ready for people to download, and use that. We should update the CI to build and upload that properly to itch.io.