Prepare release v0.13.0 (#448)

## Overview

Changes:

* Added the release date, set to next Monday (2025-01-20).

Author: Zeitsperre

CHANGELOG.rst

@@ -2,7 +2,7 @@
 Changelog
 =========
 
-v0.13.0 (unreleased)
+v0.13.0 (2025-01-20)
 --------------------
 
 * Added support for Birdhouse Helper Bot (for bumping versions).