qa: timelock coinbase transactions created in functional tests

test/functional/mining_mainnet.py

@@ -30,6 +30,7 @@ from test_framework.blocktools import (
 
 from test_framework.messages import (
     CBlock,
+    SEQUENCE_FINAL,
 )
 
 import json
@@ -61,6 +62,10 @@ class MiningMainnetTest(BitcoinTestFramework):
         block.nBits = DIFF_1_N_BITS
         block.nNonce = blocks['nonces'][height - 1]
         block.vtx = [create_coinbase(height=height, script_pubkey=bytes.fromhex(COINBASE_SCRIPT_PUBKEY), retarget_period=2016)]
+        # The alternate mainnet chain was mined with non-timelocked coinbase txs.
+        block.vtx[0].nLockTime = 0
+        block.vtx[0].vin[0].nSequence = SEQUENCE_FINAL
+        block.vtx[0].rehash()
         block.hashMerkleRoot = block.calc_merkle_root()
         block.rehash()
         block_hex = block.serialize(with_witness=False).hex()