docs: add release notes for race condition fixes

Author: ellemouton

docs/release-notes/release-notes-0.20.1.md

@@ -47,6 +47,14 @@
   or key) existed. The manager now correctly regenerates both files when either
   is missing, preventing "file not found" errors on startup.
 
+* [Fixed race conditions](https://github.com/lightningnetwork/lnd/pull/10433) in
+  the channel graph database. The `Node.PubKey()` and
+  `ChannelEdgeInfo.NodeKey1/NodeKey2()` methods had check-then-act races when
+  caching parsed public keys. Additionally, `DisconnectBlockAtHeight` was
+  accessing the reject and channel caches without proper locking. The caching
+  has been removed from the public key parsing methods, and proper mutex
+  protection has been added to the cache access in `DisconnectBlockAtHeight`.
+
 # New Features
 
 ## Functional Enhancements