Update changelog for #8433

Author: JonoPrest

CHANGELOG.md

@@ -51,6 +51,7 @@
 - Run `super_errors` fixtures in parallel (~2.4× faster locally). https://github.com/rescript-lang/rescript/pull/8430
 - Expand `super_errors` fixture coverage for the remaining reachable single-file error variants. https://github.com/rescript-lang/rescript/pull/8432
 - Cache OPAM env, rewatch build, and instrumented dune state in the coverage workflow. https://github.com/rescript-lang/rescript/pull/8434
+- Add a multi-file fixture harness (`super_errors_multi`) for cross-module errors and warnings. https://github.com/rescript-lang/rescript/pull/8433
 
 
 # 13.0.0-alpha.4