chore: Add a changelog entry for GHSA-x958-rvg6-956w

Author: poljar

crates/matrix-sdk-crypto/CHANGELOG.md

@@ -6,6 +6,11 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased] - ReleaseDate
 
+### Security Fixes
+- Check the sender of an event matches owner of session, preventing sender
+  spoofing by homeserver owners.
+  [#13c1d20](https://github.com/matrix-org/matrix-rust-sdk/commit/13c1d2048286bbabf5e7bc6b015aafee98f04d55) (High, [GHSA-x958-rvg6-956w](https://github.com/matrix-org/matrix-rust-sdk/security/advisories/GHSA-x958-rvg6-956w)).
+
 ### Bug Fixes
 - Remove a wildcard enum variant import which breaks compilation if used with
   `tracing-attributes` version `0.1.29`. This is a workaround for a bug in