refactor: Simplify access to attribute_co_authored_by

Co-authored-by: aider (vertex_ai/gemini-2.5-pro-exp-03-25) <[email protected]>

Author: ei-grad

aider/repo.py

@@ -217,7 +217,7 @@ def commit(self, fnames=None, context=None, message=None, aider_edits=False, cod
             attribute_committer = self.attribute_committer
             attribute_commit_message_author = self.attribute_commit_message_author
             attribute_commit_message_committer = self.attribute_commit_message_committer
-            attribute_co_authored_by = getattr(self, "attribute_co_authored_by", False) # Should be False if not set
+            attribute_co_authored_by = self.attribute_co_authored_by
 
         # Determine explicit settings (None means use default behavior)
         author_explicit = attribute_author is not None