test: use f-strings in feature_cltv.py

Author: fanquake

test/functional/feature_cltv.py

@@ -135,7 +135,7 @@ def run_test(self):
         block.nVersion = 3
         block.solve()
 
-        with self.nodes[0].assert_debug_log(expected_msgs=['{}, bad-version(0x00000003)'.format(block.hash)]):
+        with self.nodes[0].assert_debug_log(expected_msgs=[f'{block.hash}, bad-version(0x00000003)']):
             peer.send_and_ping(msg_block(block))
             assert_equal(int(self.nodes[0].getbestblockhash(), 16), tip)
             peer.sync_with_ping()
@@ -173,8 +173,7 @@ def run_test(self):
             block.hashMerkleRoot = block.calc_merkle_root()
             block.solve()
 
-            with self.nodes[0].assert_debug_log(expected_msgs=['CheckInputScripts on {} failed with {}'.format(
-                                                block.vtx[-1].hash, expected_cltv_reject_reason)]):
+            with self.nodes[0].assert_debug_log(expected_msgs=[f'CheckInputScripts on {block.vtx[-1].hash} failed with {expected_cltv_reject_reason}']):
                 peer.send_and_ping(msg_block(block))
                 assert_equal(int(self.nodes[0].getbestblockhash(), 16), tip)
                 peer.sync_with_ping()