docs: update release notes

Author: ellemouton

docs/release-notes/release-notes-0.21.0.md

@@ -70,7 +70,8 @@
   need for maintenance as the sqlc code evolves. 
 * Prepare the graph DB for handling gossip V2 
   nodes and channels [1](https://github.com/lightningnetwork/lnd/pull/10339)
-    [2](https://github.com/lightningnetwork/lnd/pull/10379).
+    [2](https://github.com/lightningnetwork/lnd/pull/10379) 
+    [3]().
 
 ## Code Health