sha3: add changelog entry for v0.10.9 (#838)

Author: newpavlov

sha3/CHANGELOG.md

@@ -27,6 +27,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 [#798]: https://github.com/RustCrypto/hashes/pull/798
 [#815]: https://github.com/RustCrypto/hashes/pull/815
 
+## 0.10.9 (2026-04-19)
+### Fixed
+- Non-compliant initialization of cSHAKE when serialized length of function name and
+  customization string is a multiple of the block size ([#836], backport of [#834])
+
+[#834]: https://github.com/RustCrypto/hashes/pull/834
+[#836]: https://github.com/RustCrypto/hashes/pull/836
+
 ## 0.10.8 (2023-04-08)
 ### Fixed
 - Performance regression: now uses `p1600` fn ([#472])