Pin actions/checkout action to b4ffde6

Author: renovate[bot]

.github/workflows/auto-merge.yaml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout source
-        uses: actions/checkout@v4
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4
 
       - name: Create app token
         id: create-app-token