CHANGELOG: add entry for patch 1255

Author: dannywillems

CHANGELOG.md

@@ -32,6 +32,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **Development Tools**: Enhanced formatting infrastructure with MDX file
   support and trailing whitespace management
   ([#1234](https://github.com/o1-labs/openmina/pull/1234))
+- **Development tools**: Add shellcheck to the CI
+  ([#1255](https://github.com/o1-labs/openmina/pull/1255))
 
 ### Changed