ci: Checkout repo when publishing index manifest

Author: Techassi

.github/workflows/build.yaml

@@ -162,6 +162,11 @@ jobs:
       id-token: write
     runs-on: ubuntu-latest
     steps:
+      - name: Checkout Repository
+        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+        with:
+          persist-credentials: false
+
       - name: Publish and Sign Image Index
         uses: stackabletech/actions/publish-index-manifest@29bea1b451c0c2e994bd495969286f95bf49ed6a # TODO: Use released action
         with: