test: verify post-restart IS lock on all nodes, not just sender

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: UdjinM6

test/functional/p2p_instantsend.py

@@ -214,7 +214,8 @@ def check_mn_peers(node=mn_node, my_hash=mn_info.proTxHash):
         is_id = sender.sendtoaddress(receiver_addr, 0.5)
         self.bump_mocktime(30)
         self.sync_mempools()
-        self.wait_for_instantlock(is_id, sender)
+        for node in self.nodes:
+            self.wait_for_instantlock(is_id, node)
         self.log.info("InstantSend lock succeeded after full restart")
 
         # clean up