fix(utils): adjust witness count calculation logic

Updated the witness count calculation in `testnet_cleanup.py`.

Author: mkoura

cardano_node_tests/utils/testnet_cleanup.py

@@ -251,7 +251,7 @@ def return_funds_to_faucet(
         txins, skeys = flatten_tx_inputs(tx_inputs=batch)
         fund_tx_files = clusterlib.TxFiles(signing_key_files=skeys)
         batch_tx_name = f"{tx_name}_batch{batch_num}"
-        witness_count_add = max(2, len(skeys) // 20)
+        witness_count_add = max(2, len(skeys) // 10)
 
         # Try to return funds; don't mind if there's not enough funds for fees etc.
         try: