Build releases for M1 via GitHub Actions

[memcorrupt]

The current build system only creates macOS binaries for x64. From my research it should be possible to make CMake build FAT binaries for x64 and ARM64 by placing the following directive before the project directive:

set(CMAKE_OSX_ARCHITECTURES "arm64;x86_64" CACHE STRING "")

Testing on an M1 machine confirms this works, but I've opted to open an issue instead of a PR since this requires testing to ensure it works with other platforms, and the Makefile would also have to be updated for builds via make. Additionally, it could be more beneficial for the flag to be added into only the GitHub Actions workflow files.

To use the current Luau releases from GitHub, M1 users must install Rosetta and use the x64 version that is currently published; therefore, this improvement would allow a better experience for M1 users.