add missing type hint

Author: miguelgrinberg

elasticsearch/dsl/search_base.py

@@ -721,12 +721,13 @@ def ensure_strings(
 
         def ensure_strings(
             fields: Union[
+                bool,
                 str,
                 "InstrumentedField",
                 List[Union[str, "InstrumentedField"]],
                 Dict[str, List[Union[str, "InstrumentedField"]]],
             ],
-        ) -> Union[str, List[str], Dict[str, List[str]]]:
+        ) -> Union[bool, str, List[str], Dict[str, List[str]]]:
             if isinstance(fields, dict):
                 return {k: ensure_strings(v) for k, v in fields.items()}
             elif isinstance(fields, bool):