Update change log for release.

Author: kmvanbrunt

CHANGELOG.md

@@ -1,3 +1,9 @@
+# 2.5.3 (November 5, 2024)
+* Enhancements
+  * Changed `CommandSet._cmd` to a read-only property which never returns `None` because it
+    is meant to be called after the `CommandSet` is registered. This addresses type checker
+    errors that occurred if `CommandSet._cmd` wasn't cast or checked if `None` before use.
+
 # 2.5.2 (November 3, 2024)
 * Bug Fixes
   * Fixed default `pytest` execution when not using cmd2's custom `invoke` command via `inv pytest`