[chronik] Fix chronik_spent_by test

Summary: This was landed by the time D13771 was being worked on and was missed.

Test Plan:
With and without chronik:

./test/functional/test_runner.py chronik_*

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D13773