Adding one more 'Visible for testing' comment

Author: schmidt-sebastian

packages/firestore/src/local/indexeddb_schema.ts

@@ -642,6 +642,7 @@ export const V1_STORES = [
   DbTargetDocument.store
 ];
 
+// Visible for testing
 export const V2_STORES = V1_STORES;
 
 const V3_STORES = [...V2_STORES, DbClientMetadata.store, DbTargetChange.store];