electron-builder names the unpacked output <os>-unpacked on x64 and
<os>-<arch>-unpacked elsewhere (linux-arm64-unpacked, win-arm64-unpacked).
install.sh desktop_product_present and install.ps1
Test-DesktopProductPresent only listed the x64 names, so a rerun on an
ARM64 desktop install skipped the desktop rebuild and left a bundle built
from the previous code. List every unpacked dir main_desktop.py already
resolves, in both installers.