Consider channel in buildConfig first
Consider channel in buildConfig first

fixes https://github.com/brave/browser-laptop/issues/10515

Auditors: @bsclifton, @aekeus

Test Plan:
1. CHANNEL=beta npm run build-package on windows
2. And open Brave in Brave-win32-x64
3. Go to about:brave
4. Channel should be beta

luixxiul/browser-laptop,luixxiul/browser-laptop,luixxiul/browser-laptop,luixxiul/browser-laptop,diasdavid/browser-laptop,diasdavid/browser-laptop,diasdavid/browser-laptop,diasdavid/browser-laptop