[doc] Upgrade the message overview (main branch exclusive)

Author: Pierre-Sassoulas

doc/user_guide/messages/messages_overview.rst

@@ -380,6 +380,7 @@ All messages in the convention category:
    convention/compare-to-zero
    convention/consider-iterating-dictionary
    convention/consider-using-any-or-all
+   convention/consider-using-augmented-assign
    convention/consider-using-dict-items
    convention/consider-using-enumerate
    convention/consider-using-f-string