test: fix non-determinism in p2p_headers_sync_with_minchainwork.py

The test for node3's chaintips needs some sort of synchronization in order to
be reliable.

test/functional/p2p_headers_sync_with_minchainwork.py

@@ -49,7 +49,7 @@ class RejectLowDifficultyHeadersTest(BitcoinTestFramework):
 
     def test_chains_sync_when_long_enough(self):
         self.log.info("Generate blocks on the node with no required chainwork, and verify nodes 1 and 2 have no new headers in their headers tree")
-        with self.nodes[1].assert_debug_log(expected_msgs=["[net] Ignoring low-work chain (height=14)"]), self.nodes[2].assert_debug_log(expected_msgs=["[net] Ignoring low-work chain (height=14)"]):
+        with self.nodes[1].assert_debug_log(expected_msgs=["[net] Ignoring low-work chain (height=14)"]), self.nodes[2].assert_debug_log(expected_msgs=["[net] Ignoring low-work chain (height=14)"]), self.nodes[3].assert_debug_log(expected_msgs=["Synchronizing blockheaders, height: 14"]):
             self.generate(self.nodes[0], NODE1_BLOCKS_REQUIRED-1, sync_fun=self.no_op)
 
         # Node3 should always allow headers due to noban permissions
@@ -78,7 +78,7 @@ class RejectLowDifficultyHeadersTest(BitcoinTestFramework):
             } in chaintips
 
         self.log.info("Generate more blocks to satisfy node1's minchainwork requirement, and verify node2 still has no new headers in headers tree")
-        with self.nodes[2].assert_debug_log(expected_msgs=["[net] Ignoring low-work chain (height=15)"]):
+        with self.nodes[2].assert_debug_log(expected_msgs=["[net] Ignoring low-work chain (height=15)"]), self.nodes[3].assert_debug_log(expected_msgs=["Synchronizing blockheaders, height: 15"]):
             self.generate(self.nodes[0], NODE1_BLOCKS_REQUIRED - self.nodes[0].getblockcount(), sync_fun=self.no_op)
         self.sync_blocks(self.nodes[0:2]) # node3 will sync headers (noban permissions) but not blocks (due to minchainwork)