CI: make sure staging is always first so it takes precedence

.github/workflows/main.yml

@@ -52,9 +52,10 @@ jobs:
       - name: Add staging repo
         shell: msys2 {0}
         run: |
-          sed -i.bak '1s|^|[staging]\nServer = https://repo.msys2.org/staging/\nSigLevel = Never\n|' /etc/pacman.conf
+          cp /etc/pacman.conf /etc/pacman.conf.bak
           grep -qF '[clang32]' /etc/pacman.conf || sed -i '1s|^|[clang32]\nInclude = /etc/pacman.d/mirrorlist.mingw\n|' /etc/pacman.conf
           grep -qF '[clangarm64]' /etc/pacman.conf || sed -i '1s|^|[clangarm64]\nInclude = /etc/pacman.d/mirrorlist.mingw\n|' /etc/pacman.conf
+          sed -i '1s|^|[staging]\nServer = https://repo.msys2.org/staging/\nSigLevel = Never\n|' /etc/pacman.conf
 
       - name: Update using staging
         run: |