Fix type of synchronize_session in update and delete methods (#76)

Currently, it's annotated as a str. Nevertheless, the argument can also be a bool.

See parts in doc for update and delete: https://docs.sqlalchemy.org/en/14/orm/query.html#sqlalchemy.orm.Query

Author: TilmanK

sqlalchemy-stubs/orm/query.pyi

@@ -167,11 +167,11 @@ class Query(
     def merge_result(self, iterator: Any, load: bool = ...) -> Any: ...
     def exists(self) -> Exists: ...
     def count(self) -> int: ...
-    def delete(self, synchronize_session: str = ...) -> int: ...
+    def delete(self, synchronize_session: Union[str, bool] = ...) -> int: ...
     def update(
         self,
         values: Any,
-        synchronize_session: str = ...,
+        synchronize_session: Union[str, bool] = ...,
         update_args: Optional[Any] = ...,
     ) -> int: ...