[test] fix broken interface_usdt_utxocache.py test
Summary: Broken in D13670
Test Plan:
cmake .. -GNinja -DENABLE_TRACING=1 ninja sudo ./test/functional/test_runner.py interface_usdt_net sudo ./test/functional/test_runner.py interface_usdt_utxocache sudo ./test/functional/test_runner.py interface_usdt_validation
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D16022