fix: Update sdk.firestore.yml (#15867)

Author: ncooke3

.github/workflows/sdk.firestore.yml

@@ -34,6 +34,7 @@ jobs:
     outputs:
       changed: ${{ steps.firestore_src_changes.outputs.sources == 'true' || steps.related_changes.outputs.other_changes == 'true' }}
     steps:
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
       - uses: dorny/paths-filter@de90cc6fb38fc0963ad72b210f1f284cd68cea36 # v3.0.2
         id: firestore_src_changes
         with: