Update extensions.mdx

Author: aritchie

src/content/docs/release-notes/extensions.mdx

@@ -20,6 +20,9 @@ import RN from '/src/components/ReleaseNote.astro';
 
 ## Extensions
 
+### 1.3.1 - September 19, 2025
+<RN type="fix">Type and AsSelf was being ignored if a base class is being used</RN>
+
 ### v1.3.0 - September 16, 2025
 <RN type="enhancement">DI registration now supports `AsSelf` which allows an implementation to be registered directly</RN>