chore: update changelog for release

Author: SimenB

CHANGELOG.md

@@ -11,15 +11,21 @@ project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
+### Added
+
+[unreleased]: https://github.com/siimon/prom-client/compare/v15.1.2...HEAD
+
+## [15.1.2] - 2024-04-16
+
+### Changed
+
 - Add `Registry.PROMETHEUS_CONTENT_TYPE` and `Registry.OPENMETRICS_CONTENT_TYPE` constants to the TypeScript types
 - Correctly read and set `contentType` top level export
 
 ### Added
 
 - Enable `bun.js` by catching `NotImplemented` error (Fixes [#570](https://github.com/siimon/prom-client/issues/570))
 
-[unreleased]: https://github.com/siimon/prom-client/compare/v15.1.0...HEAD
-
 ## [15.1.1] - 2024-03-26
 
 ### Changed