Changelog entry

Author: anakinj

CHANGELOG.md

@@ -11,6 +11,7 @@
 **Fixes and enhancements:**
 
 - Fix compatibility with the openssl 4.0 gem [#706](https://github.com/jwt/ruby-jwt/pull/706)
+- Test against Ruby 4.0 on CI [#707](https://github.com/jwt/ruby-jwt/pull/707)
 - Your contribution here
 
 ## [v3.1.2](https://github.com/jwt/ruby-jwt/tree/v3.1.2) (2025-06-28)