use max-parallel to avoid Elasticsearch indexing congestion (#32804)

.github/workflows/sync-search-elasticsearch.yml

@@ -34,6 +34,7 @@ jobs:
     runs-on: ubuntu-20.04-xl
     strategy:
       fail-fast: false
+      max-parallel: 3
       matrix:
         # This needs to match the languages we support
         language: [en, ja, es, pt, cn, ru, fr, ko, de]