build: update to btcwallet version with async mempool scan

This version of btcwallet demotes some spammy logs (txns replaced in the
mempool), and makes the initial mempool scan async.

Fixes https://github.com/lightningnetwork/lnd/issues/7640

docs/release-notes/release-notes-0.16.2.md

@@ -0,0 +1,12 @@
+# Release Notes
+
+## Wallet
+
+[The mempool scanning logic no longer blocks start
+up](https://github.com/lightningnetwork/lnd/pull/7641). The default polling
+interval has also been increased to 60 seconds.
+
+## Bug Fixes
+
+[A panic has been fixed](https://github.com/lightningnetwork/lnd/pull/7637) for
+neutrino nodes related to sweeper transaction replacement.