Code sign macOS binary

[epompeii]

Currently the macOS binary requires a security exception to run because it is not signed.
Add code signing to the CI build process: https://melatonin.dev/blog/how-to-code-sign-and-notarize-macos-audio-plugins-in-ci/

[BD103]

Note that this costs $99 yearly for an Apple Developer Account. Furthermore, this popup has only happened to me when I launch an application through Finder, not when I execute it in the terminal. I would probably prefer signing the binaries using PGP instead, which is cross-platform and far less expensive.