chore: pin GH Actions to commit sha

rancher/rancher-security 1906

Signed-off-by: Derek Su <derek.su@suse.com>

Author: derekbit

.github/workflows/sync-upstream.yml

@@ -9,7 +9,7 @@ jobs:
   repo-sync:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5
       with:
         persist-credentials: false
     - name: repo-sync