cowork-bot: SHA-pin actions/checkout in cowork-auto-pr workflow

Author: Coding-Dev-Tools

.github/workflows/cowork-auto-pr.yml

@@ -16,7 +16,7 @@ jobs:
       # without this step every run failed with "not a git repository" and no
       # PR was ever opened (fleet-wide defect: 11/11 seeded copies lacked it).
       - name: Check out the pushed branch
-        uses: actions/checkout@v4
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262  # v4.2.2
         with:
           ref: ${{ github.ref_name }}
           fetch-depth: 0