(trivial) wallet: fix stale comment on on_event_invoice_status

The followup rename (_paid_invoice_keys -> _paid_invoice_keys_cache) and
the de-sloppify left this comment referring to the old name and claiming
the listener only tracks LN-driven changes; it is now the population path
for onchain invoices too.

Author: sashazykov

electrum/wallet.py

@@ -662,7 +662,7 @@ def on_event_adb_removed_verified_tx(self, adb, tx_hash):
 
     @event_listener
     def on_event_invoice_status(self, wallet, key, status):
-        # keep _paid_invoice_keys in sync with LN-driven status changes
+        # keep _paid_invoice_keys_cache in sync with all invoice status changes
         if wallet != self:
             return
         if status == PR_PAID: