CI: use the staging repo
CI: use the staging repo

This should allow us to build against packages already merged
but not in the repo.

waterlan/MSYS2-packages,mati865/MSYS2-packages,JPeterMugaas/MSYS2-packages,Alexpux/MSYS2-packages,mati865/MSYS2-packages,JPeterMugaas/MSYS2-packages,mati865/MSYS2-packages,atom2013/MSYS2-packages,Alexpux/MSYS2-packages,JPeterMugaas/MSYS2-packages,waterlan/MSYS2-packages,waterlan/MSYS2-packages,Alexpux/MSYS2-packages,JPeterMugaas/MSYS2-packages,atom2013/MSYS2-packages,mati865/MSYS2-packages,waterlan/MSYS2-packages,Alexpux/MSYS2-packages,atom2013/MSYS2-packages,atom2013/MSYS2-packages