Docs: Update CHANGELOG.md with notes of v0.21.11

Author: sphuber

CHANGELOG.md

@@ -52,6 +52,15 @@ This release applies the fixes that were released on the support branch of `v0.2
 - Update the `mypy` pre-commit dependency [[#246]](https://github.com/aiidateam/plumpy/pull/246)
 
 
+## v0.21.11 - 2024-07-01
+
+### Fixes
+- Make `Waiting.resume()` idempotent [[a79497b]](https://github.com/aiidateam/plumpy/commit/a79497ba37cef7bc609cee90535ad86708fc48f9)
+
+### Dependencies
+- Add requirement `nbdime<4` [[94df0df]](https://github.com/aiidateam/plumpy/commit/94df0dfd0a3ea93174aa4de83ac5e06246350c27)
+
+
 ## v0.21.10 - 2023-11-13
 
 ### Dependencies