ci: use checkout v6

Author: SapphoSys

.github/workflows/arch-source-package-smoke.yml

@@ -26,7 +26,7 @@ jobs:
           echo 'builder ALL=(ALL) NOPASSWD: ALL' > /etc/sudoers.d/builder
 
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Check .SRCINFO is current
         run: |