Include architecture in filenames of Windows and macOS GitHub assets

[agateau]

Is your feature request related to a problem? Please describe.

I packaged GitUI for Clyde, a package manager for prebuilt applications. It is difficult for Clyde to guess the architecture of the Windows and macOS GitHub assets because they are named gitui-win.tar.gz and gitui-mac.tar.gz.

Until now those where x86-64, but in the latest release (0.26.2), the mac asset switched to aarch64.

Describe the solution you'd like

Assets should be named gitui-win-$ARCH.tar.gz and gitui-mac-$ARCH.tar.gz.