release-notes: update for 0.19.0

docs/release-notes/release-notes-0.19.0.md

@@ -221,6 +221,9 @@
   these options have also been increased from max 3 log files to 10 and from 
   max 10 MB to 20 MB. 
 
+* Refactored the `ValidationBarrier` to use
+  [set-based dependency tracking](https://github.com/lightningnetwork/lnd/pull/9241).
+ 
 * [Deprecate `dust-threshold`
 config option](https://github.com/lightningnetwork/lnd/pull/9182) and introduce
 a new option `channel-max-fee-exposure` which is unambiguous in its description.