[DOC] Update changelog

Author: f-dangel

changelog.md

@@ -14,6 +14,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fix CI (apply latest `black`, use latest `pytest` and `pytest-benchmark`)
   ([PR](https://github.com/f-dangel/backpack/pull/348))
+  - Follow-up fix, isolating a test that re-produces a memory leak.
+    Always run the full test suite
+    ([PR](https://github.com/f-dangel/backpack/pull/349))
 - Improve efficiency of Hessian-vector product
   ([PR](https://github.com/f-dangel/backpack/pull/341))