fix: Use utils.json_iso_dttm_ser to dump jsons when async query execu…

…tion (#13830)

* Use utils.json_iso_dttm_ser to dump jsons

If encoding is not `None`, the default encoder `utils.json_iso_dttm_ser` is not used for binary data and instead tries to encode to the default 'utf-8'. 
This fixes #13829

* Change to comply with tox -m pre-commit

superset/views/core.py

@@ -2172,7 +2172,9 @@ def results_exec(  # pylint: disable=too-many-return-statements
             obj = apply_display_max_row_limit(obj, rows)
 
         return json_success(
-            json.dumps(obj, default=utils.json_iso_dttm_ser, ignore_nan=True)
+            json.dumps(
+                obj, default=utils.json_iso_dttm_ser, ignore_nan=True, encoding=None
+            )
         )
 
     @has_access_api