ci: bump actions/checkout to v7 (Node 20 deprecation), SHA-pinned

Author: ice-chillios

.github/workflows/auto-update.yml

@@ -12,7 +12,7 @@ jobs:
   update-invoicy:
     runs-on: r5n-m2-ultra
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
 
       - name: Check for Invoicy update
         id: check