Update django_mongodb_backend/introspection.py

Jib's suggestion

Co-authored-by: Jib <Jibzade@gmail.com>

Author: WaVEV

django_mongodb_backend/introspection.py

@@ -42,8 +42,8 @@ def _get_search_index_info(self, table_name):
                 type_ = VectorSearchIndex.suffix
                 options = details
             else:
-                columns = list(details["latestDefinition"]["mappings"].get("fields", {}).keys())
                 options = details["latestDefinition"]["mappings"]
+                columns = list(options.get("fields", {}).keys())
                 type_ = SearchIndex.suffix
             constraints[details["name"]] = {
                 "check": False,