Fix Typo attr -> attrs (#20400)

George-Ogden · web-flow · commit 12d53f688e9b · 2025-12-11T12:11:30.000-08:00
In the example, `attrs` is used, even though `attr` is imported.
Picking either one isn't important, but the code gives a runtime error
when the other one is used.
diff --git a/docs/source/additional_features.rst b/docs/source/additional_features.rst
@@ -135,7 +135,7 @@ Type annotations can be added as follows:
 
 .. code-block:: python
 
-    import attr
+    import attrs
 
     @attrs.define
     class A:
