Add version & date to changelog

Author: imjoehaines

CHANGELOG.md

@@ -1,15 +1,12 @@
 Changelog
 =========
 
-## TBD
+## v4.6.1 (2023-12-11)
 
-### Enhancements
+### Bug fixes
 
 * Avoid using deprecated `flask.__version__` attribute
   [#365](https://github.com/bugsnag/bugsnag-python/pull/365)
-
-### Bug fixes
-
 * Ensure the session delivery queue is started regardless of `auto_capture_sessions` configuration
   [#367](https://github.com/bugsnag/bugsnag-python/pull/367)