docs: update release note for itest ctxt fix

docs/release-notes/release-notes-0.15.0.md

@@ -6,6 +6,12 @@
   for running lnd alongside a bitcoind service is now provided in
   `contrib/init/lnd.service`.
 
+## Code Health
+
+### Code cleanup, refactor, typo fixes
+
+* [Refactored itest to better manage contexts inside integration tests](https://github.com/lightningnetwork/lnd/pull/5756).
+
 # Contributors (Alphabetical Order)
 
 * Daniel McNally