Update keyless-connections.md SearchClient arg

The SearchClient takes in `index_name`, not `index`.
https://learn.microsoft.com/en-us/python/api/azure-search-documents/azure.search.documents.searchclient?view=azure-python

Author: mikkeyboi

articles/search/keyless-connections.md

@@ -196,7 +196,7 @@ credential = DefaultAzureCredential(authority=authority)
 
 search_client = SearchClient(
     endpoint=service_endpoint, 
-    index=index_name, 
+    index_name=index_name, 
     credential=credential, 
     audience=audience)