Update index.mdx (#8159)

Author: renebrandel

src/pages/[platform]/build-a-backend/data/custom-business-logic/search-and-aggregate-queries/index.mdx

@@ -905,7 +905,7 @@ You can also check this in the DynamoDB console by going to the Integrations sec
 
 ## Step 4: Expose new queries on OpenSearch
 
-### Step 4a:Add OpenSearch Datasource to backend
+### Step 4a: Add OpenSearch Datasource to backend
 
 First, Add the OpenSearch data source to the data backend. Add the following code to the end of the `amplify/backend.ts` file.