Add release notes for code-cleanup PRs

Author: oschwald

CHANGELOG.md

@@ -5,6 +5,8 @@ CHANGELOG
 ------------------
 
 * First release using Central Portal instead of Legacy OSSRH.
+* Improve internal uses of types and other code cleanups. Pull requests
+  by Philippe Marschall. GitHub #246, #247, #248, and #249.
 
 3.1.1 (2024-09-19)
 ------------------