🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Author: gcf-owl-bot[bot]

google/api_core/rest_helpers.py

@@ -81,7 +81,10 @@ def _flatten_value(obj, key_path, strict=False):
 
 
 def _flatten_dict(obj, key_path, strict=False):
-    items = (_flatten(value, key_path=key_path + [key], strict=strict) for key, value in obj.items())
+    items = (
+        _flatten(value, key_path=key_path + [key], strict=strict)
+        for key, value in obj.items()
+    )
     return functools.reduce(operator.concat, items, [])