Update CHANGELOG.md for release 2.13.1

Author: isc-pbarton

CHANGELOG.md

@@ -5,7 +5,7 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [2.13.1] - Unreleased
+## [2.13.1] - 2025-09-16
 
 ### Fixed
 - Fixed Import All deploying changes to files in a CSP application (#828)