test: fix intermittent issue in feature_bip68_sequence

To avoid `bad-txns-premature-spend-of-coinbase` error,
when getting a utxo (using `get_utxo`) to create a new
transaction `get_utxo` shouldn't return by default
immature coinbase.

test/functional/mempool_compatibility.py

@@ -47,12 +47,12 @@ class MempoolCompatibilityTest(BitcoinTestFramework):
         # unbroadcasted_tx won't pass old_node's `MemPoolAccept::PreChecks`.
         self.connect_nodes(0, 1)
         self.sync_blocks()
-        self.stop_node(1)
 
         self.log.info("Add a transaction to mempool on old node and shutdown")
         old_tx_hash = new_wallet.send_self_transfer(from_node=old_node)["txid"]
         assert old_tx_hash in old_node.getrawmempool()
         self.stop_node(0)
+        self.stop_node(1)
 
         self.log.info("Move mempool.dat from old to new node")
         old_node_mempool = os.path.join(old_node.datadir, self.chain, 'mempool.dat')