fix: use actions/checkout@v6 for rock packing

Author: edisile

.github/workflows/pr.yml

@@ -79,7 +79,7 @@ jobs:
     permissions:
       contents: read
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Setup LXD
         uses: canonical/setup-lxd@main