docs: update release notes for gossip v2 graph preparation

Add reference to the PR implementing v2 channel support in the graph
database layer.

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

@@ -176,9 +176,10 @@
 * Freeze the [graph SQL migration 
   code](https://github.com/lightningnetwork/lnd/pull/10338) to prevent the 
   need for maintenance as the sqlc code evolves. 
-* Prepare the graph DB for handling gossip V2 
+* 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](https://github.com/lightningnetwork/lnd/pull/10380).
 
 ## Code Health