message: test: use f-strings in feature_segwit.py
diff: @@ -65,7 +65,7 @@ def find_spendable_utxo(node, min_value):
  if utxo['spendable']:
  return utxo
  - raise AssertionError("Unspent output equal or higher than %s not found" % min_value)
  + raise AssertionError(f"Unspent output equal or higher than {min_value} not found")
  txs_mined = {} # txindex from txid to blockhash
  