Update changelog

Author: bgrant

CHANGELOG.md

@@ -4,6 +4,9 @@ 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).
 
+# [Unreleased]
+- [PR 133](https://github.com/salesforce/django-declarative-apis/pull/133) Handle missing related instance in filter caching
+
 # [0.29.0] - 2023-08-16
 - [PR 129](https://github.com/salesforce/django-declarative-apis/pull/129) Remove outdated HttpResponse wrapper